We are looking in to adding an affiliates program for the new site. The question is, wich one should we get?

We need one that handles and tracks affiliate links properly and flawlessly. It needs to have a CP for both affiliate and admin, and a way for the affiliates to choose banners/buttons to add to their websites. Another important feature is the look. It needs to look top notch, preferably a nice clean look.

Paid or free, wich one would you recommend and why?