The one that you find that makes you money. Why? Because you found it and started making money. There is not a best one around. People make money selling hosting, mens enhancement, or web design. Its what makes you money. I make a ton selling some of the stupidest things people would not think twice about. Affiliate marketing is nothing but a new term for commission sales.
Second line of my sig combines 6 of the best affiliate programs online and they set you up with a website that is ready to take orders within 24 hours. Check it out if you want the best!
It's just as easy to promote a high paying affiliate product as it is to promote a low paying one. The best paying one is the one I'd be promoting if I were you.
Whatever interests you and you can find a way to sell is the best product for you. For me, the best product is my own because I know how to sell it