I mostly do low level roulette, so I have gotten into the habit of checking the search info of everyone and seeing who's actually new and who's just leveling an alt or running roulette (assuming you can't tell just by their gear). I try to give my commendations to the new players first, regardless of role. In Trials and Expert roulette I try to give it to DPS since we don't get as much love. Although, when I'm running as healer, I find myself giving my commendations to the other healer in 8 mans as a sort of "My fellow healer" kind of thing.