Mine's pretty simple - I generally tend to punt the ones I'd have no chance with in real life, or with the ones that offer services you'd not likely get in real life (or for fear of getting your arse kicked if you had the balls to ask!). So for me, that's girls younger than I could pull (as in 18-22ish - but I'm equally happy punting a more mature woman in her 40's too - as long as she hasn't let herself go
), slim (but not skinny; with some curves is always good), and pretty. Blonde, brunette, red head, not too fused. English, EE, again not fussed - I've had good punts with both English and EE's, and bad punts with English and EE's too. I think I prefer smaller tits to huge ones, B/C/D mainly, although a nice DD is always a bonus.
Most of all, I just want them to be pleasant, and not jaded hags. Granted, I know they are here for the money and not to make friends, but the ones that actually act like they enjoy the time with you, are pleasant, polite and fun, are more likely to get my money a second, third or fourth + time