If leads and affiliate sales are a major source of revenue, it is important to find reliable businesses/ websites to work with. Very often, your affiliate commission gets stolen, if the minimum payout is $25, you do not have a single conversion for months once you reach $24. And when you remove the affiliate link from your website, the affiliate manager starts frantically emailing you.
Lead generation is better, you can atleast forward the same lead to another company / competitor and also warn the buyer about the supplier who has cheated you. An example of what people do when promises are not kept.
http://www.david-carter.com/wp/2009/11/the-real-power-of-domain-development/