As you would imagine, the more characters that synergize within your team, the better. Here are some other things to consider:
Your point character probably has teammates that help them out, but if you’re not fine with your point character dying first or if they get snapped out, do they have assists/DHCs/Alpha Counters to help out the other character(s) on your team?
If there’s a particular character you really don’t want dying on your team, do you have a safe DHC or a good Alpha Counter option to get them out of danger?
Is there a character that gives two/three characters in your team a tough time? Do any of your characters bring support options to deal with this matchup? This game has less than 20 characters that are all perfectly viable, so don’t count on any rarely seen matchups.
Do any of your characters have more than one assist option you can pick to deal with different teams? If you play any of The Glue Characters, the answer is probably yes.
Is my starting team order good? Can I change it to deal with certain roundstart matchups better?
Does my team fall apart if a certain character dies first? Do I have at least two (in both duo and trio) characters that can fight solo without too much trouble?
Great synergy across all characters, and you can play this team in different orders so you're never truly in a bad spot even when you tag, DHC, or get snapped. Parasoul and Fukua have lower damage than the rest of the cast, but can easily tag in to Painwheel to get more damage and run your momentum with her, backed up by two great assists.
Peacock and Umbrella love Hairball assist, Peacock and Filia both get nice usage out of Cliif Hanger, and everyone loves L George assist. This team has plenty of safe DHCs thanks to both Peacock and Umbrella, with plenty of combo DHCs as well.
One of the game's best battery characters to fuel two characters who are very strong with meter, one of the game's best middle position characters with one of the game's best lockdown assists, and a powerful anchor character who can supply either lockdown/space-control or an armored overhead assist to those in front. The Squigly/Eliza shell is very sturdy with the Lady of Slaughter into Squigly Battle Opera DHC having nice applications for safety or combo damage in either order, and Fortune very much likes both of their assist kits.
Fortune and Beowulf compete for the point position, but having Fortune start out to land a hit and then tag/DHC into Beowulf so that he can get his game started is a solid gameplan. The issue is that Fortune and Beowulf have awful synergy, relying on Big Band to keep the team together. If you're playing against an opponent who takes note of this, they will simply snap in Big Band to kill him first, and it's not like Big Band will have stellar assists to help him out. Even glue can't fix a tossed Playstation 4 controller if you're missing the DPad.
There are some strategies such as treating Beowulf as the fake anchor and letting Valentine play neutral first, and having Painwheel mid is always a good option. The assist synergy however is decent at best all across the board. Might fall into the "bad" team category depending on who you ask.
The various forms of what's known as "Team Viable", as you have characters who all want the point or mid position, but none of them are great anchors. Not a good team, not even a bad team, just "viable".
Less of a "team" and more just three selfish point characters coming together to fight the enemy. No character on this team really likes either of the others as a partner with their below average assists, and you have very little utility through DHCs without impressive damage to make up for it. The only real saving grace is that Fortune and Valentine are very strong characters... but with this team they may as well be playing solo. Everyone will cheer for you if you play this team because this is probably the worst team in the game, and you are a trooper for sticking to it.
This is honestly maybe the only trio team I'd say is outright bad. There are some teams that can come pretty close to this, but usually all that's needed is an assist or order change and that team is gucci again.
“It’s so simple to fix a team in this game. You can’t take any team in this game, and then tell me that I can’t replace one of those characters and make it a good team.”