My first and foremost favorite is Noble. Why? There's not 2000+ people playing in FR's. Their limit is 500 and that's a good thing for two reasons. One- you don't fall asleep just waiting for people to knock themselves out. Two- The less people there are in a tourney, the bigger 1st prize is for you.
My 2nd favorite site is Absolute. While they may allow thousands of people to register for their Freerolls, I find their software easy to navigate. AND- sitouts (people who don't show) are eliminated after so long of sitting out.
That's my favorite sites.