I use NetVerifier, CyberAge and Sexkey.
NetVerifier works best for me and I use it for larger sites with recurring income like
http://www.eatabeaver.com/firsttime/
I use CyberAge for basic smaller sites that don't give rebills like
http://www.eatabeaver.com/cathteen/ NetVerifier used to have basic sites but they've scrapped them.
I use Sexkey for sites I want to a lot of advertising on, they let you advertise pretty much anything anywhere including sites from other AVS's. I build them similar to free sites, with the second page only advertising Sexkey and the inside pages full of ads like
http://www.eatabeaver.com/nakedgypsy/ first content page is
http://www.eatabeaver.com/nakedgypsy/diddle.htm Also Sexkey sends more traffic from their link list than any of the others. NetVerifier sends a bit, and CyberAge sends almost none.
I like mixing them up so I can sell surfers from one AVS memberships to other AVS's, but if I had to stick to just one I'd use NetVerifier since they pay the best and recur longer than any paysite I've ever promoted.
If I can help any way just let me know.