I usually run as the healer or the tank, and I don't commend the support roles until they really stood out. My criteria for which dps gets the comm goes as follows:

* Performed well in the instance. If they are new, they listened to direction or were quick to learn.

* Threw a funny Bloodborne reference at me. Points are deducted if they throw a "It would please me to use the doll." No. Bad. This stopped being funny five years ago. You actually get anti-comms for this (I will find a way to make you die).

* Were generally pleasant and funny. Talking in a dungeon is actually a huge plus for me, and if you have a good attitude that really stands out to me. I don't even care if you ate every AOE in sight, if you are just a fun person to have in the party then you get that headpat.