I think it depends on what kind of site you plan to advertise on. For sites in niches that have very high adsense CPC, then you may make more money with adsense. But if it is a site targeted on a specific niche where there are a lot of potential buyers, then clickbank may make you more money. Its best to experiment, like try one month with adsense, then one month with clickbank and see which one makes you more money.
Clickbank is better because commisions can be as low as $5 to a whopping $200. Adsense clicks requires a lot of traffic which can be a downside if you dont have a good ranking.