I'd like to throw my hat into the ring here too, but really.... search the various message boards for recommendations. When you find a good one, search them again to see if they pay timely.
Also, feel try to sign up for 2 or 3 of them and see which you prefer.
I have worked with Hydra, Xy7, Neverblue they all have worked well for me if you know your markets. It is all about finding the right deal for you and who has it. On that note please check out the thread i started regarding signing up at other places!