I'm not so sure of the $50 price gap... Stormer lists the 12R5 for $199 and the GenX for $224.
I just bought a new GenX at 360 Speedway for $199, and they threw in the wide rear pod kit with it. I'm pretty sure they still have one left on the wall at that price.
As far as:
Racing: completely agree with AreCee
Handle: completely agree with AreCee
Overall: completely agree with AreCee
Which one is better? I have to say the GenX is WAY better, because I just bought one.
Seriously, just like AreCee said, both cars are excellent, I doubt you'd go wrong with either one. If I were going to choose one right now, I'd look at which car had better parts support locally. Actually, I can think of one other factor... If you have all metric tools, go for the 12R5. If you have all Imperial sized tools, go for the GenX. If you have both, or don't mind buying some tools, it's back to both are great cars, take your pick.