I make more money with Clickbank than I do with AdSense, that is for sure. But there may be some situations where AdSense ads perform better. For example if you have a blog with a lot of different topics... You would want to use AdSense since it will adjust to your topics with related ads. But if you are really hammering home one thing and there's some high converting CB products related to that one thing, you'll probably do better with Clickbank.
As stated by ZIBBlu It's better to get 100 Adsense clicks than 100 CB clicks without sales. You have to know your visitors. If they are wiling to spend money on CB products - go for it. If not, then Adsense is the way to go.
If you have a web site or blog related to some topic and if you find suitable products in clickbank, then it is better to use Clickbank Ads rather than adsense.