I recommend Adsense for beginners who want some income, and pros who actually bothered to master it, but... It seems like Adsense is an easy solution, perhaps too easy. For real big profit potential which do you prefer Adsense or Affiliate programs? Why??
I think it depends on the subject of the site. For instance, a Flash arcade site that's popular would still probably earn more from a relevant affiliate program than from AdSense. Also, a Web hosting-related site would earn more from hosting affiliate programs than from AdSense. But, a general-interest forum would do better with AdSense. So, it really depends on the subject of the site.