"I just started and I don't know which avatars to buy. Help?"
Help is here. In this section, I will list each of the major avatars, packs, or sets that are considered "meta", in approximate order of overall usefulness and purchasing priority, particularly to new players. If you want to read through the set-by-set analysis which displays each avatar in the game and their individual ratings instead, click here.
The listing you find here is merely a general consensus suggestion. Some suggestions are strong and others pretty loose and dependent on play style, but none of this is mandatory. Anyone is free to ultimately make their own decisions and adjust to your personal goals and play style. This is also not a meta-game tier-list of the avatars in the strict sense, though a lot of this will very closely mirror it. This is a combination of power in the general meta-game and both usefulness to a new player and universality of the avatars. In other words, the top listed avatar set here wouldn't necessarily be considered the top avatars of the meta-game (though very close); it is the first listing because it is both a highly regarded set in the meta and a set that most play styles would heavily use and is very beginner friendly.
The Toy Animal set. These three are a pretty big deal and staple of team building on every game mode and any skill level. They are extremely simple, and therefore supremely beginner friendly. They buff your HP and grant you a massive defense boost against one of the three tank types. Any time you are putting a new team together for the first time and find a gap where you're not sure which avatar to use, these guys will be your fail-safe go-tos. They work on every tank, in every mode, and virtually every playstyle, and require essentially no advanced understanding of the game to utilize. You cannot go wrong here as your first purchase.
The Nasty Animal set. As long you play 2v2 Score or ProBattle modes, this set is easily one of the strongest as well as easy-to-use sets to purchase as your very first avatars beyond the defaults. You are primarily buying this for Penguin and Cat in the long run, who continue to have a major presence at every level of play including the highest leagues, though even Fox is solidly usable and suitable as a straight forward damage-booster for your 3rd position tank. I place this set below the Toy Animals because they are slightly more complicated. For the most part, their abilities are passive and it's much harder to play against them properly than it is to use them properly, but even when they are on your own tanks, there are occasionally situations where understanding their triggers and effects would change what the optimal decision would be. That being said, just slapping Penguin and Cat onto tanks 1 and 2, and Fox onto tank 3, and going into battle and just focusing on shooting isn't going to cause you much trouble at all at lower leagues.
S-Koroni and the Aliens pack. S-class Koroni is one of the most vital avatars in the game, and probably has the strongest case to be made for being the top avatar in the current meta-game, at least in 2v2 and ProBattle. She grants her tank an automatic 1.5 bars of SS meter at the start of her turn if two other tanks allied with her have been destroyed. She punishes misplays by your opponent severely, combos with Penguin to enable potential turn-1 SS activation, will in any case accelerate your SS by about one turn regardlessly, can counteract and challenge the powerful SS-breaker items, and even offers some life-extending emergency restore if and when she draws focus fire. She is listed below the toys and nasty animals because acquiring her is much more difficult (assuming you do not have god-sent luck) since she is a card-pack draw rather than a guaranteed purchase. That said, no gem ever spent on the Aliens pack in attempt to get all three S-Koroni cards will ever be a gem wasted. And the upside is, while you are taking swings at S-Koroni cards, you will quickly gain access to some very usable A-class avatars from that pack. A-Koroni is still quite good but the half-bar difference in their ability is pretty gargantuan -- in high levels of play especially. Kaka and Space Lord are very similar, and function as a poor-man's Koroni in most ways. Again, Koroni is so good that even the lesser versions are still good avatars. A-class Doc M is the next biggest star here however and is also a long-standing staple of the meta from top to bottom. Doc M is the most powerful self-healer in the game and can easily fully negate the damage of an entire, well placed shot, purchasing you at least a full extra turn if he is activated.
The Victims Pack. Dargom seems to love not just making avatar sets based on animals and toys, but invariably making them exceptionally strong. These beat-up stuffed animals have found a very cozy and unique spot in the high-level meta and by their design, they tend to be really friendly toward new players too. They all have powerful abilities that activate when they are either the lowest leveled tank on the field (including being tied for lowest), or are being bullied and have the lowest current HP total. Much like the above entries, their passive abilities are strong and put the onus on your opponent to play against them smartly while you mainly get to relax and reap the benefits when they fail to do so. Here, both S-class avatars, Threads and Sad Frog, are top-notch choices for any tank at or under level 40. Unlike the gap between A and S Koroni, their A versions are not enormous downgrades and hold up quite well if you don't feel like chasing those purple lottery tickets. Poor Rabbit is hugely important as well, being, with little argument otherwise, the best heal-stealing avatar in the game. Sick of seeing Doc Ms, Mummies, and Yunins poo-pooing on your well executed assaults? Rabbit will make them regret it and tread a lot more carefully around you. The only avatar here that is a bit negligible is Troubled Monkey. It's not terrible, but it's abilities have somewhat conflicting interests, where Tired Dog or Sad Frog will fulfill the same purpose, but better.
Yunin. On paper she should be the easiest avatar to automatically and reflexively suggest to any player, old or new. She heals, herself and teammate, a lot. Her presence in higher levels of play is somewhat niche these days. She is still strong no matter what league you are in and always will be, but she's suffered from the over-exposure over the years and experienced players have built-in muscle reflexes and a photographic Rolodex of memories of getting burned by Yunin to the point where everyone knows how to dance and play around her. Everyone, of course, except inexperienced players in lower leagues. That said, even in higher leagues she has a strong presence in the hands of a player who understands that they can't just fall asleep at the wheel and expect a free downpour of heal procs. If you invest in proactive strategizing with her, she's good anywhere, any time. Here is the big catch though of course: she costs money. As in, real life dollars. 20 of them, USD. She is the only meaningful cash-only element in the game (my apologies to Roy and Anissa...and Rudolf Girl or whatever her name is). I do NOT want to levy the impression to any new player that Yunin is, in any sense, 'mandatory', nor 'overpowered/pay-to-win'. She isn't even in the top 5 meta avatars in the highest leagues these days. She is exceptionally effective against very unprepared novices or just people who are playing while half-asleep, but by the time you've spent a couple of days playing and escape the bronze league, most players are going to be forcing you to pay attention and make somewhat rational decisions in order to get use out of her. She's helpful and cool to have if you have the expendable cash, and it's not "bad" or "wrong" to support well-made free-to-play games with purchases like this as some overly-cynical players will often imply. She isn't a scummy loot-crate item, you get exactly what you pay for. And if you don't have the money or shouldn't have the money, don't buy her and don't feel bad about it for one moment.
Robo x3. Robo x3 is an interesting case. She is essentially the best defense avatar for any tank that can consistently bang out super-sky shots. Only marginally less total defense than a fully decked-out S-JewelHelmet, but gets an extra red, yellow, and purple jewel slot as a kicker. She can't be super high on this list since she requires super-sky shots, and most of the challenge of this game is learning how to do that consistently, and so she isn't friendly to freshly hatched newbies. However, she is so good and reliable for a large number of tanks that anyone who has started getting the feel for super-skies should be quickly adding her to your grocery list. There's another odd factor about her to mention as well. She is a pack-pull and has an S-class variation. However, her S-class iteration is by far the most pointless of them all. Her A-class version is identical to the S-class except that one of the abilities gives 1% less defense, and its the less important of the two abilities at that. It's actually outrageous. Just pull until you get the A-class and save yourself the headache. However, if you happen to run into one or two of her S cards in the process, I would hang onto them. There is no avatar more overdue for a sudden, overnight buff than S-Robo x3 and any given update announcement in the future is liable to make you regret extracting those cards instead of just sleeving them. Finally, Robo x3 is also odd for being in a pack that is almost useless otherwise. There are arguably some very niche uses for Robo x2, and are nothing but "neat concept but poorly executed" duds beyond it. Robo x3 is that good though. Snag an A-class and don't look back.
Carnival pack. There isn't anything majorly game-breaking in this, but it has a dearth of very flexible, very solid avatars and one that might be a sleeper hit in the near future due to a recent addition made to the blue jewels. We'll start with the sleeper. Remember how much I talked up the greatness of S-Koroni earlier? Carnival pack has it's own version of this same concept in S-Joker. Historically, S-Joker has been considered "S-Koroni, but not as good". Joker would probably be considered the best avatar in the game if Koroni just didn't exist, he's that good, and for the same reason, but he is completely neglected because Koroni's healing is decidedly more desirable than his attack power boost. With the recent advent of shot power extending blue jewels however, there is no longer a reason to think S-Joker is universally obsoleted by S-Koroni. In the case of tanks with low-end shot power who struggle to consistently reach high enough for a super-sky shot, S-Joker and his blue jewel slot might offer salvation and a better offer than the cute, pink alien girl. Joker aside, Bear has always been an upper-tier, strong and easy defensive avatar that can be slapped onto anything, anytime, guilt free. Poor Rabbit has replaced Jessica in many people's eyes as the top dog of the "Hunger" game, but she isn't so far behind that if you happen to get her before getting a Rabbit that you wouldn't offer her gainful employment. Wendy is a half-way decent bungee avatar if you happen to snag her due to an early investment in this pack, but she will be replaced down the road if you really get into the bungee business. And Edward, sweet Edward; Adorable, but useless.
Jewel Seekers. This pack has the one avatar that could rival S-Koroni for title of meta-game queen in S-JewelHelmet, an avatar that could not possibly be any simpler and beginner friendly, technically, and it's nevertheless a rather tough sell for beginners and even many novice players. The Jewel Seeker avatars have no traditional abilities; instead, they have highly concentrated jewel slots of one color for ultimate min-maxing glory. S-JewelHelmet has no abilities, but has four green jewel slots. With all four filled up with up with powerful 6% defense jewels, the math says this things gets to walk into battle with an automatic, no-strings-attached, 24% damage reduction against all attacks, all of the time (after the second tanks turns of course, which is true for all avatar jewels and abilities anyway). This avatar is a dominant force in the meta-game. While it is an S-class avatar and carries with it the difficulties of obtaining one, the real issue is obtaining the jewels. You can only get 6% defense jewels through the limited supply that slowly drips out of the highly competitive World Boss mode. You need a specific set of tanks and avatars, fully leveled and decked out, and a whole lot of time, dedication, and challenge tickets to even compete for a chance at just one of these exclusive jewels, much less four of them. Some take the alternative route of settling for 5.5%, which are still rare hits in the jewel gotcha, for a 22% defense avatar rather than 24%. Anything less than these quickly render the point and concept of S-JewelHelmet pointless. With only 20% defense, for instance, a number of regular A-class avatars are outpacing the sum effective defense and they all also offer other abilities and jewel slots. It wouldn't be a weak avatar per se, but not really worth the effort without that extra chunk of defense from those uber-rare green jewels. It's entirely up to you if you want to pursue this endeavor. Also, this is where I casually mention that this pack also has S-JewelHammer, the single best avatar for Blank enthusiasts, especially, and bungee fanatics in general. And the jewels here are much easier to obtain. So there is that. Although...
Monsters pack. Ok, S-JewelHammer is the definitive avatar for Blank, make no mistake, but this boy Purple Devil alongside her is essential for full-scale bungee team builds. Purple Devil (PD) gets the weaker one-bar version of Koroni and Joker's SS boosting ability, which is still very nice, make no mistake, but the main attraction here is the unique Hero of Shovel ability. Under the same condition (two allied tanks destroyed), PD gets a massive, permanent boon to its explosion range. It goes without explanation why this is central to bungee teams. Slap this guy on your Bigfoots and Beetle Kings and go to town. This set also has Alice Red, who specializes in countering self-healers and can be a major MVP in lower leagues in particular where Docs and Mummies are more prevalent. Yeti is balanced and simple, a strong and flexible option for some straightforward and sizable HP and damage buffs. Last longer, hit harder, easy. While you are here looking for PD, Franken can be a pretty solid lead-tank avatar on your bungee team if you need a stop-gap while gathering the resources to assemble an S-JewelHammer. Wolfguy doesn't offer anything too special or exciting. If this is your first pack you invest into and he happens to be the first and only strictly offensive avatar on hand, he's fine enough in that role until something better comes along.
The Rest. This list isn't comprehensive. There are plenty of worthwhile avatars that haven't yet been mentioned (GuanYu and Daiochan from the Three Kingdoms set, C-Knight, FoxRain, etc.). But this list is long enough as it is. By the time you get this far and have made even half the purchases listed here, you will have enough experience under your belt to not need the guidance of an article like this and can make your own independent judgements of what you want, don't want, need, and so on. So I hope this helped, and remember, for more specialized/advanced strategies and questions on anything GBM related, come find us on the discord and ask away!