I usually follow a pattern. First and foremost whether or not they have the courtesy to give a simple, "hello" at the beginning and, "thank you" at the end. Since I almost always run as a healer, after that it'll usually go to the tank if they held aggro well enough and mitigated/dodged accordingly. If not then I usually give it to any Foe-Requiem-playing-Bard otherwise I just kinda give it to whichever person didn't leave immediately, provided they weren't awful.

I kinda wish DPS meters were a thing so I could measure performance in that regard and commend accordingly.