This is my experience from doing 50/55 trials, haven't touched 60 stuff yet:
Depends on what dungeon and the role. For general trash clearing, AoE is preferred greatly, AoE will generally always outdamage a single target DPS on trash. AoE melee DPS is a bit funny. BDs aren't as great as mages due to they can't constantly AoE and you need to be centered in the middle of the mob pack and if the tank is doing a big pull, your AoE attacks don't have enough range to hit every mob whereas a snowstorm does. Samurais I haven't seen too many of being level 55, but have seen a few in 55 trials, they seem to be good but it's hard to hit every mob due to the fact their attacks are in a line as opposed to a giant circle. They do however do some nice damage to make up for it, but I can't really talk on samurais seeing as I haven't played one yet.
For bosses, MAs really do wreck bosses fast from what I've seen. Thieves aren't liked that much and there's certain bosses where I would say where I want a DPS to go ranged instead. An example of this would be Karen in Venin T. Karen uses a roar debuff, if you hit her with it on you'll heal her for 40k. It however is an AoE and it's around her, so it'll only hit melee DPS and the tank. It's not a problem if the MA or melee DPS is half awake, but a lot of melee DPS get tunnel vision syndrome and will heal the boss. If the melee DPS has half a brain and is aware of their surroundings then it's not so bad. Another example is Chino also in VeninT, Chino uses an AoE knockback which will generally only hit melee. But a lot of melee DPS attack Chino's back and when they get hit with the AoE knockback they go flying backwards, get stunned and the DoT that Chino also may kill them because a lot of healers will ignore the melee DPS going across the screen and focus on purifying winding the tank and healing the ranged DPS/healers around them from the DoT. But generally a melee DPS is good on any boss I've encountered as long as the melee DPS has half a brain and the healer spams AoE heals and purifying wind.