Dark Side for better damage and strength equipment.
All skill checks in the game are possible to do with 10 intelligence. As we will be under Valor as often as possible, we will want odd numbers so it ends up even. This is much more important for Strength, Wisdom and Charisma. Attribute modifier from gear, useable, alignment and such is limited to +10 (20 strength) but base attribute isn't included, which means that the best possible strength modifier would be with 17 starting strength for 22 by level 20. We're going to be at 15, losing only a single modifier for much better power DC and survivability.
15 Strength (Str)
13 Dexterity (Dex)
13 Constitution (Con)
10 Intelligence (Int)
13 Wisdom (Wis)
13 Charisma (Cha)
Level 4-8-12-16-20 all on strength for best damage. Other possibilities would be to lower either Dexterity, Constitution, Wisdom or Charisma for 17 strength or 14 intelligence (2 skill points per level as a guardian) if one prefer being skilled, which was my initial build. Still even with 2 less DC and lower HP, it ended up as strong as Insanity worked on everything i needed to and HP would barely go down at all (a defeated foe cannot hit you). 12 intelligence can also be done if you're afraid of missing experience for level 19 before the Leviathan. This would mean being able to reach level 10 repair instead for level 17.
Persuade have the highest number of skill checks in the game. To achieve 100% persuasion chance on hard checks, which are pretty rare in the game but still present, we will need to be able to achieve 6 persuade points higher than our character level. This isn't possible even it it is a class skill as it has a maximum of clvl +3, we will however be able to make the check under Knight Valor for 16 charisma, netting a +3 persuade bonus.
The other meaningful checks are only with Repair as Computer Use isn't needed for the Mandalorian Weapon Cache side quest on Korriban as there is no need to induce catatonic state this time. Rest of the checks are only for spike costs and can be done with party members.
Now for Repair it is trickier than the LS build as we are not getting it as a class skill. Skill points of a 10 int scoundrel is more than enough for both Persuade and repair, even a bit for demolition, however experience min-maxing will be required to achieve level 19 or 171000 xp before the Leviathan. This would mean: Finish Taris at level 9 to get a free xp boost to 10 once becoming a jedi, kill everything you can, get the best quest outcome even if it doesn't give you DS points like destroying the Harvesting Machine on Manaan, help the wounded wookie to get defeat the hidden mandalorians on Kashyyyk, help the sand people, bring them the pearl then kill them after, do all companion quests (i managed to get it without doing Threat from Xor), use your repair parts on the droids you see, do all quests and side quests but the Tomb of Naga Shadow on Korriban. As i remember, an unfixed game can max their level using T3-M4 to access the restricted data repeatively on the dueling terminal on Korriban.
Now for the skill per levels:
Persuade maxed on all level ups;
Keep 22 total skill points for repair which will need to be at 11, max it when available (level + 3 / 2);
You should have another 8 points left to put where you want. I recommend Demolition for an easier time recovering/disarming mines without having to switch gear. I personnally went with 7 Demolition and 1 Security to save some time opening doors and lockers while damage is low. If going with 14 intelligence, Treat Injury can also be interesting as we will not have a self heal and Drain Life/Death Field will be taken last. We should always have a companion with Cure available for us however and the build rarely loses any HP in the end.
Awareness has a wisdom bonus and your companions can make the check for you, which will allow you or another party member to disarm/recover the mine.
Just like the LS build, every single point of defense will make a big difference during Taris. Make sure to Queud normal attacks in combat before switching character to avoid the -5 defense penalty of critical strike, which we will use on target that we will kill in a single round or debilitated foes only.
Scoundrel levels (do not level past level 7):
Level 1 : Two Weapon fighting.
Level 2 : Implant 1
Level 5 : Improved Two Weapon Fightning
Granted feats: Improved Scoundrel Luck at level 6 (+4 defense), Sneak Attack IV at level 7 (4-24 extra damage on enemies hit at the back or immobilized)
Jedi Guardian levels (should be level 10 total after training if you did all side quests on Taris, repaired some of the remaining droids at a high character level and killed everything including Gadon):
Level 1: Master Two Weapon Fighting
Level 3: Implant 2
Level 6: Improved Critical Strike
Level 7: Master Critical Strike
Level 9: Implant 3
Level 12: Weapon Focus: Lightsaber or Toughness
Level 13: Weapon Specialization: Lightsaber or Improved Toughness
Granted feat: Master Force Jump (+4 attack and damage per attack, trigger sneak attacks), Master Sense (+6 Defense), Jedi Defense (Can deflect blaster bolts using a lightsaber, we will not bother with this at any time).
You can either choose to get a bit more HP and damage reduction or to deal more damage. A force jump will usually deal more average damage using a Baragwin Assault Blade in the main hand with a lightsaber in the off hand, however most enemies on the Star Forge and Unknown World Temple have a Dark Side alignment, which makes a Mantle of Force + Solari + Phond more worth it in the main hand instead with even stronger Master Critical Strike damage. Force jump with BAB in main hand have 20% chance for a critical hit, while only 10% with the lightsaber. However Master Critical Strike has 50% chance for the BAB and 40% for the lightsaber, which will have more damage vs Dark Side on top.
Level 1 (8): Force Speed, Energy Resistance
Level 2 (9): Knight Speed
Level 3 (10): Improved Energy Resistance
Level 4 (11): Fear
Level 5 (12): Horror
Level 6 (13): Insanity
Level 7 (14): Force Resistance
Level 8 (15): Master Speed
Level 9 (16): Force Valor
Level 10 (17): Drain Life
Level 11 (18): Death Field/Force Immunity
Level 12 (19): Knight Valor
Level 13 (20): MasterValor
Insanity is way more effective than many would think despite the low DC of our build as the majority of enemies in the game has very poor Will save compared to Fortitude and for the very few who are immune or save the effect, you'll be better off one shotting them in melee instead. Will work on anything you'll need it to work on even with those attributes, especially buffed by Valor.
If you're not going for Death Field and only Drain Life for the captives on the final fight, you can choose Drain Life at the very end or something else entirely if you want to let Malak break all the captives instead, which is still a very safe approach in the end.. Force Resistance is still very effective if you prefer Death Field as most enemies but the strongest one are going to be below your level. As mentionned however, HP will barely go down and the dark jedi on the Star Forge usually start their first round with Force Resistance or Immunity, which you will have to breach using Bastila. Our DC is also pretty low, which will result Death Field being saved often, which is why i prefered Immunity on my latest playthrough.
Energy resistance again on a high priority for the same reasons as the LS build: because the improved version will also absorb the first 15 points of energy damage (and other elemental damage) of any attack, which is unlisted but calculated on feedback (energy resistance will not, only the improved version). This is calculated before the difficulty multipler so on RCM Impossible, it effectively absorb 45 energy damage per attacks for a 120 seconds duration for all of your party members.
The scout or soldier can definitely work well for a guardian build, it doesn't bring anything to the table in the end however. We get maximum damage against Malak using Master Critical Strike (especially that he has Improved Toughness, reducing 2 damage per damage type), we don't need any more feats and we can still fully repair HK without having Repair as a class skill so we would only lose a ton of damage (4-24) and defense (4). Scout level 3 is also pretty pointless in term of feats as you're limited to Empathy or Conditionning, we easily hit maximum accuracy anyway so Soldier is also pointless. Scoundrel having Persuade as a class skill, making all checks easy to pass is the cherry on the cake. It also destroy any duelist on the Taris Dueling Ring during a single stun period Bendak included, thanks to Concussion Grenades.
Absolutely, however the Guardian LS Mastery bonus get wasted as bonuses to strength cap at +20 (+10 modifier) and we still get it as DS. I would advice following my Consular guide instead, which is a nice change of pace. Insanity would also cost way more FP, which can hurt for a Guardian. Stasis is a bad idea due to Fortitude Saves being the highest one from the majority of enemies in the game, especially tough ones.