I pick whoever is nicest if I can. (If I feel talkative enough to say Hiya at the beginning of the run, next person who says hi and doesn't suck gets it. :P)

Failing that, I'll pick someone that does a little more. Healers that DPS, DPS that drill down whatever is punching the healer when the Tank is otherwise occupied, stuff like that.
And if nothing else, I'll default to a healer or a tank (whoever did their job better.)
If everyone else sucked, or pissed me off somehow, nobody gets it!