I evaluated all affiliate scripts and programs before launching our affliate program for a FREE/PAID subscription service...
my advice,, build it yourself.
When you build it yourself you can credit affiliates based on transactions. We pay our affiliates a reccuring amount, (hard to find in any software or program)
with these scripts you usually end up wasting lots of time cutting and peicing code together. The concept of an affilaite is very simple to program.
Our service gives our affiliates tracking tools, banner and ad choices, url shorteners, marketing tools, and a 3 tiered structure that promotes our affiliates signing up their friends as affiliates.
We are soon going to join the Google Affiliate Network, and Linkshare. Both will allow us to keep our own (BETTER) affiliate software. We are using Google and LInkshare to gain better exposure to new affiliates. Our google and llinkshare plans will pay a 95% commission on the first months transaction, whereas our own product pays 25%. (300% per year). The reason for this is to attract and convert those affiliates from other networks..