I can’t help too much from an affiliate point of view (yet) but from a player point of view, I can’t see as there is too much to choose between Playtech or Cryptologic.
My two favourite sites as a player were/are Intercasino and Totesport. The customer support for both is fantastic and, if you are regular, the rewards you can get are awesome.
Inter run a lot of regular competitions and usually offer pretty regular “extra” deposit bonuses with pretty low wagering requirements. I’ve also had a few good days out courtesy of them. Totesport do similar and are very good at ticket/event prizes. I’ve had countless racing and football tickets from them (including a pair of tickets to the Carling Cup Final) and they also took me to Vegas earlier this year for the darts tournament.
Assuming you’re on a rev share deal and want to promote places that hang on to their players and get the best value out of them, I can’t recommend these two highly enough.
Hope this helps.
*edit* – just to clarify, though I’m sure everyone knows! Intercasino are on Crypto, Totesport on Playtech. Obvious down-side is neither take US players. Tote also don’t have a poker room, whereas Inter do.