The Infinity is basically a Prime with improved Wifi and GPS signals. The trade-off is entirely up to you.
I have a Prime and I love the thing. It's razor thin, feels extremely sturdy, the screen is amazing, and it's super fast. BUT, I'm really bummed about the GPS issues. I cannot get a lock and Asus is no longer giving out a free dongle (not that I want one anyway). So, I'm actually on the hunt for a cheap Infinity in the US.
But if you have no interest in using your tablet for GPS, then you might save yourself some money and go with the Prime. It's really a beast!