I generally commend in the following order:

1 - Someone who made the dungeon fun and entertaining, even if they weren't a great player.
2 - First timers and sprouts.
3 - Someone who was REALLY good at their job.
4 - DPS
5 - Healers
6 - Tanks
7 - Whoever is still left after the rest of the party insta-leaves before I can even click a name.