For my commendations, I like to give them to DPS because I know as a DPS, I have a hard time getting them (I saved us from a wipe once and I didn't get any ;O; ). But if I had criteria it would be: if you say hello at the start (I like conversations even if it's just a hello and good job at the end), if you do your job really well (that makes me go "I wish you were on my server"), if you make me laugh. If everyone's even or if none of the criteria are met, I throw one to a DPS unless they annoyed the crap out of me.