The best ad network depends on your site type and results. In reality you need to check which is the best network for YOU. Google Ad Sense can be good for one site but bad for another. The issue here is try and see. There are others ad networks that might give more infromation like ad brite, and etc. (I can give you the full list if you like of most of the known companies). If you are a forum on a certain product (such ipod) you might need to check other sites that are more designated to this kind of product. All in all it is just depends on what is on your site...and your traction