~ How much experience do you have with R/C cars?
Ultimately, it's your setup, engine tuning and driving ability that will decide how well you do on the track. Each car you listed has the potential to cross the finish line first, but their design, durability, reliability and how easy they are to work on the pit table are not the same.
My Knowledge Base site has quite a bit of info on the RRR, MTX-4 and 720. That might help with your with your decision.
I would also suggest that you download the manual, setup guide and setup sheet for each car and read through them carefully. It will give you a better understanding of the differences between each car.
Good luck - and let us know what you decide.