I if I have the time will evaluate every player on the instance. IF I find they generally help me out as a tank, such as virusing adds, debuffing a boss, really good dps, heal really well, I'll hand out commendations. But the primary motivator will be kindness. IF I see a player being helpful especially if we have a new person, then I'll hand out a commendation to them as well. I hand out commendations to all players not just the healer.