Bard is the cookie cutter subclass that's useful for leveling/luring but gets less useful as you go on in levels.
Ravager is good for aoe/cleave and whatnot, but is lacking in defensive/healing/single target.
Gunslinger is good for pvp/pve(with appropriate funding/gear) but lacks in self healing/defense(provides ranged/burst and utility, and decent dps)
Sorcerer is a noticeable DPS increase, and has great utility for both pvp/pve, lures, self healing, minor aoe, good single target, not much in the way of defense. Ranged
Wizard - burst/dps, ranged stun/leap(more useful than you'd think) and very minor self healing, ok single target and amazing AoE, not much in the way of defense.
Grenadier - very minor potential healing(for party!) hands free dps increase + ranged/utility, not much for defense.
Duelist - decent single target DPS w/ dots you can easily stack, low survivability, has a distance closer but otherwise no ranged, minor to no self healing or AoE
Imo, for PVE, Sorcerer and Gunslinger are pretty decent choices, while bard is better for low end pve or running without bards, but tends to be less impressive later on, ravager is fun/useful in certain situations but doesn't "shine", Wizard is good for pvp/burst aoe, Grenadier is unique and possibly fun, Duelist would be decent DPS and you usually won't have to worry about main class duelists competing with you in debuffs/dots(since they die/aren't invited to parties v_v)
Note that just about any class combo can be useful with the right gear, but as a slow melee tank, the things I find myself lacking aren't defense, but self healing, ranged, and burst. Most tanks want to get melee for fullturtledeathmode but there are often times*coughzaahir* where meleeing, even as a tank, isn't the best of choices.
"Kirito does the best dps from behind!"
Formerly known as IceCreamMan - Guardian/Gunslinger in Aura Kingdom.