Oh, the fun stories I could tell you about this topic. Blogged about it a couple days ago too. I know lots of affiliates that have taken their AS links down or moved them to bottom of page and then suddently start getting affiliates sales. One affiliate I know built an app to use datafeeds purely for back fill content to generate more AS$, didn't even think about making commission. Checks started coming in from the affiliate links, much to his surprise. Another one of my affiliates had Adsense ads filling the top of the page for one of our highest converting programs with an average order size of $300. The datafeed links were 2 screens down and he could not figure out why he was not making commission while other affiliates were converting at 1:30.
But basically the key is testing and it comes down to the affiliate program's payout and conversions. If you can make one affiliate sale every 100 clicks that pays an average $36 commish vs getting 5 cents a click and only make $5 for the same 100 visitors then the affiliate program will earn you more. But some affiliate programs don't convert so you'd make more with AS. You really just need to test different merchants and different ad placement to see what earns the most.