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It really depends on what industry you are in. I think every industry/niche has some "best" Merchants... (They are called Merchants, not Affiliates). They are called Merchants because they are the ones who sell the product... whatever that is. They do the orders, shipping, payment, etc. Affiliates are those of us who promote their product, and get a cut... but don't have to deal with all the other crap :-]
For instance... The Match.com one you mentioned is supposed to be a really good merchant in the dating niche. I wouldn't be promoting Match.com on a site that is about selling army equipment. You want relevancy.
As for Amazon, I have not heard many good things about them. They cap their commissions, and their pay sucks.
But back to your main question... There really is no best Merchant. It all depends on what niche you are dealing with.
All the Best,