Marketing is about finding markets and fulfilling customer needs. Picking a product then hoping you can find a market is a recipe for failure! The "Best" programs are the one you can actually market.
Personally I like Amazon Associates and ClickBank. Didn't have much luck with eBay Partner Network or any other affiliate programs.
Unregistered, is "Amazon Associates" just selling using basic amazon affiliate or are there varying ones?
There's no best affiliate program. Just join a respected, top rated program and promote their products.