I don't give commendations based on performance. Well, maybe, but here's basically the hierarchy:

1. Someone who pulls off an amazing feat that basically saves the entire party/dungeon/raid. This can be done by a party member in ANY role.
2. Someone who amuses me. Usually by chatting.
3. Someone who says anything at all that isn't negative.
4. A DPS.
5. Coin flip between tank or healer.

So whichever happens first on my list gets the commendation. ^.^