For me it is
CyberAge . They convert well for me. I do a lot of ultra niche type of things and I think the people that join my platinum sites like that not only am I offering them this site that they never thought they would find but I am also offering them a bunch of mainstream stuff through the other sites on Cyberage.
They also retain like mad, I have had maybe 2 people cancel before I got atleast one rebill out of them but on some of my fetish sites I have people that have been rebilling for seven months or more.
Their rules are pretty liberal but what I really like is that they answer emails. If you have a problem with not being put on the list, which I have had a couple times recently, you just use their contact form and they usually respond back to you within 24 hours.
The link lists traffic is good stuff. I, like many, use it to feeder sites to upsell memberships and it does work.