Balance issues aside, which kit do you think is the most fun / best gameplay design?

I'm having the most fun with my power-based Scorpion-Kroguard. Whoever decided to give him 2 priming abilities on top of charge is a hero.

I really like the angara avenger.
Avenger strike is an awesome teleport, to kill shit, to get to shit and to get away from shit.
Invisibility is awesome for any objectives. Best escape skill there is. Also helps your team mates in certain situations.
Granade is an awesome big boom for dmg.
Passives are also nice. Survivability and some weapon dmg.

Current favorite is my Angara Avenger.

i really like the turian havoc trooper. she has a unique niche as the first and only Mass Effect character that specializes in aerial combat/bombardment.
human kineticist also has a very unique kit that has a relatively high skill floor and cap. i'm concerned that any buffs to biotic abilities/combos will inadvertently make her overpowered.

Asari Adept, Asari/Human Sentinels, Krogan/Human Vanguards, Angara Insurgent
And the Krogan Engineer will be nice too when they fixed tech combos
And I'd love the Salarian Architect with Energy Drain instead of Barricade

Asari Duelist - because I love biotic charge and swords

I only played 4 characters.
Human Inf, adept, Kroguard and AAdept.

I found human adept most fun to play with.

Good team support, useful pull, nice crowd control.. and good punch.

She is not good against multiple armored enemies... but I never gave her a good gun or double damage ammos so I think I can work with that.
Other than that.. useful and effective in every game for every team.

Human adept for me. It would be much much better if the cool down on singularity was a bit shorter. I also like the asari adept but lance stinks and I think I would get owned on gold if i tried that class because you need to play aggressively with ann field.

Cloak helps your teammates find more enemies, if they are having trouble doing so on their own.  Extended Duration is a good evolution for that purpose.

Here's my SI.

I use Energy Drain offensively to strip as much Shields as possible, before opening fire.  He doesn't really do combos unless using Disruptor Ammo, so I just spec for Energy Drain Radius and Effectiveness.  Grenades and Passives are spec for Armor Damage.  So basically Cloak > Energy Drain > Shoot > Throw Anti Armor Grenade, or if running Disruptor Ammo, Cloak > Shoot > Energy Drain (Tech Burst) > Shoot some more > Throw Anti Armor Grenade.

Here's my HI.

This guy is different, in that he has Incinerate instead of Energy Drain.  So I spec the Grenades for Shield Damage, open with that, and use Armor Damage Incinerate at the end.  So that's like Cloak > Throw Anti Shield Grenade > Shoot > Anti Armor Incinerate (Detonates whatever Ammo Booster you are using).  It's worth noting that the HI also gets the Munitions Training 6a defenses debuff, making high rate of fire weapons preferable on this kit since each shot stacks the debuff.

Both are equally viable and I really don't consider one strictly better than the other.  Those Anti Armor Grenades for the Salarian though are rather nice for taking out Berserkers.  It's like Genophage in a can.

Not sure yet. Still waiting for vegasflash to tell me what the gud players use.