I've only ever used ClickBank. It is reliable, pays well (depending on the products obvs), and is very easy to use as it is free and all you need to do is sign up and hook up your payment details
my only criticism is their are not a lot of "great" products to sell in some niches
weight loss, fitness, and finance are niches with a lot of great products therefore their easy to sell, however, I work in the music niche, and the products just aren't that great with very 'scammy' and cheap looking landing pages which just don't convert that well.