My newbie experience over the last few weeks (midwest US location):

Deepbit is expensive, but has fast payout and is reliable
Slush seems to work best for me in terms of yield, stats are a bit basic
.LC is free but slow, functionality still a bit rough. Maybe later.
Guild is "free" but whines about donations, feels slow and did not yield as much as expected

Try each for a few days and measure how much they pay out. The bigger your sample size, the more accurate the results.