When I tank I typically give it to the healer.
When I dps I typically give it to the tank.


My decision on who I give it to, is not even necessarily decided by who did the better job. Like if I am running as damage, and the tank of the group did an excellent job, but he/she has crown next to their name..I give it the healer if they have the sprout symbol. A crown most likely has more for the achievements you get for them, so the sprout needs it more.
Or another scenario - if the healer did an excellent job and the tank was kinda...sloppy..I give it to the tank. Just from assuming that he/she is new to the role, and I don't want them to feel discouraged and decide to only run groups as a dps role after that one bad run.

I do not often give it to one of the dps players in the group, only because it can be hard to tell which one of them was putting out more damage. But when one stands out and you can easily tell the difference between them, I'll give it to that one.

Tho iv also ran in groups, where one of the dps was stepping too far off to the side and getting adds on them, and either the healer or the tank confronted them about it, in very rude ways...that kind of thing ticks me off. So come the end of the group, I give it to that player.