If you have your own product, you have something that's unique rather than being one of a thousand or ten thousand similar sites. Use this to your advantage, and it'll be much easier to market to the public, and get press and media attention.
Affiliate programs change their terms, companies go out of business, or change their products.
Build your site around somebody else's product, and you're at mercy of somebody else's decision processes. You're the center. If you join an affiliate program there are probably several thousand other affiliates in the same or similar programs, all of which are, to a greater or less degree, your competitors, and none of which will go out of their way to help you. You own the customer. So if you're an affiliate you've either got to find an endless supply of new customers, or cross your fingers and hope that people will bookmark your site before clicking on the affiliate link.