I would say, without hesitation,
Evil Genius Cash
We only have two sites, but we've built them to convert and retain. Instead of spending money on generic front ends with all the same content in the back, we've taken these niches and made them overall more profitable.
Our big and natural tit site is ON FIRE with both conversions and retention. Our monster cock site is converting and retaining well beyond our dreams and making a lot of cash for us and our affiliates.