Parts availability is always something to consider. If you LHS carries the parts that's great. The GenX has been around a bit but unless your LHS carries parts in stock for it you'll need to order them. The 12R5 is still new on the market and I imagine parts availablity will be good for them in the future but it's probably a bit light right now. One thing to consider though is both of them use very little standard parts. That being parts that are based on the older 12L designs. So there isn't much cross platform support except for maybe the rear axle. Many of the other companies like BMI, Darkside, Diggity and others, still use the AE Dynamic Strut front end, AE style rear axle, and in many cases even the rear pod plates. This makes parts availability a bit easier. I guess it really boils down to what parts you local shop carries.