Best
Adept - Drell and Smashdept
Soldier - N7 Destroyer
Sentinel - Turian
Engineer - Salarian and turian
Infiltrator - Shadow (but all of them represent the class well)
Vanguard - Smashguard
Worst
Adept - none
Soldier - Geth trooper and vorcha
Sentinel - Volus merc
Engineer - Talon merc
Infiltrator - none
Vanguard - Volus
I agree...Volus suck!
Best
Adept - N7 Fury
Soldier - N7 Destroyer
Sentinel - Turian Sentinel
Engineer - Quarian (Male)
Infiltrator - Geth Infiltrator
Vanguard - N7 Slayer
All of these picks are fairly easy to explain. An Adept should be able to handle any enemy, at any distance, without having to rely on weapons. No Adept does it better than the Fury, because she's effective with all her powers against any defense. I thought about the Asari Adept (AA), but Stasis isn't effective against armor, so it's obvious that the Fury has the edge here. Close-range, longe-range...doesn't matter for the Fury.
The Soldier class was a little harder to pick, since the Fat Turian is another great choice here. I gave the N7 Destroyer the edge here, because of his great croud-control ability. Therefore, he is using weapons to great potential, and he has grenades and/or missiles. He's basically a walking Turret or a small Atlas.
Turian Sentinel, because of Tech Armor + Warp + Overload. Easy pick!
Quarian (Male) Engineer simply because of sheer power. Amazing tech explosions are a must for any serious Engineer. Remember, an Engineer is supposed to be a specialist...much like Adept with Biotic abilities. As with the Fury, what gives the QME an edge is versatility. He can handle any enemy, at any range, at any given time. That, along with his ability to soften up the enemy with Tac Scan, ensures that the QME puts all his Engineer brothers and sisters to shame. I was thinking about the Salarian Engineer here, but he isn't as hard-hitting as the QME.
Geth Infiltrator is an easy pick, as well. All that weapon damage, bonusses, and Proxy Mine. No contest!
Versatility is a key word here, and the N7 Slayer is easily one of the most versatile kits in the game. A great hit-and-run character, the N7 Slayer is therefore a true Vanguard. He's also fantastic at any given range. For the Vanguard class, it's not a prerequiste to set-up explosions as much. They are the ultimate detonators, and nobody does it better than the N7 Slayer.
Worst
Adept - Volus
Soldier - Vorcha
Sentinel - N7 Paladin
Engineer - Vorcha
Infiltrator - Asari Huntress
Vanguard - Volus
Volus Adept was freakin' easy. Too little potential for Biotic Explosions, because he doesn't set them up very well. Not effective against armor, at all. Therefore, the Volus needs to rely on weapons and specific ammo a little too much. There's no way you can call this guy a Biotic specialist. A true Adept should be able to do most of its damage through their Biotic Powers. The combination of Biotic Mosquitoes and Stasis isn't a very good one.
Vorcha is an easy pick for worst Soldier. Relies on a Tech Power for his damage output, and isn 't that special with weapons, plus he can be pretty flimsy.
N7 Paladin should have been an Engineer. All Tech Powers, a Tech Shield...no Biotics...not a Sentinel.
Vorcha Engineer is just a weird kit. I feel he should have been the Soldier, and the Sentinel should have been the Engineer. As I said, an Engineer needs to be fantastic and powerful with their Tech Powers. Strong Fire Explosions are a must for a Vorcha Engineer, which this kit lacks to say the least. No specialist should ever have sissy Tech Bursts that the Vorcha Engineer sets-up and sets-off He should have been a Soldier, because he has that potential and it makes sense.
Another easy pick is the Asari Huntress. She's a fantastic kit, but purely Biotic. All the other Infiltrators fit the description of what an Infiltrator should be far better.
Volus really suck as Biotics. Hence, why I picked the Volus here. Sure, I could have been harsh on the Turian Cabal for the lack of Biotic Charge, but she has everything on the Volus. The Cabal survives better, is a hard-hitter, can stun certain enemies, charge through thin walls, restore Barriers, etc. The Volus is just a Volus. Not a hard hitter...one tiny misstep, and you're dead...an Biotic Orbs: I hate those light bulbs that float around the Volus like flies that are attracted to ****. Amen.