As an Affilliate, would prefer the 20%.
2nd tier signups don't happen very often and of those that do signup, they don't normally produce.
Our jobs as affiliates are to get the SHOPPER to our site, pre-sell, and get them out the door and over to the merchant. Most SHOPPERS have no idea what an affiliate program is. If the SHOPPER is an affiliate, they more than likely will buy under their own link or that of an associate and never come to another affiliate's site to shop...
It's time to go big, or go home...