It's too hard to compare. I have one with many thousands of uniques and it consistently earned pennies from Adsense. When i finally found the right affilliate oppty it started converting very well... better than adsense ever would.
5 high value conversions per day from XXXX uniques kicks Adsense's butt every day of the week.
Affiliate links can be very profitable, especially when there's a close fit between your content and the affiliate program: e.g., an affiliate link to Elbonianboatpasses.com in an article on Elbonian boat travel, or to product listings at widgetcentral.com in a test report about widgets.
However, if you have a diverse site (an editorial site, for example), not every page will be a close fit for an affiliate program. That's where AdSense comes to the rescue: If you've got an article on Elbonian boat travel and there's no affiliate program related to that topic, you can monetize the page with AdSense ads for "Elbonian boat tours," "Elbonian boat passes," "Elbonian boat discounts," etc.