I have used both and there are things I like and things i don't like about each of them. I like ClickBank even though I had to make several sales before I got that first paycheck. I like PayDotCom even though I had a problem with one vendor who just never paid me the commission I was owed.
If there is a product that I'm interested in promoting, I don't really care what company they are with, ClickBank or PayDotCom. But if they are listed with PayDotCom I try to email them before I start to promote their product. If they don't respond, I don't do business with them.