For me, I'd like to know the kind of conversions that the site gets (and retention rate) more so than the commission.

In my opinion, a site that has a 10% conversion with 50% commissions is much more attractive than a site with 1% conversion at 70%.
Plus, if the retention is good (i.e very few members quit) then I would be more than happy with 50%

Hope this helps,

Richard