There isn't really a "best" 1/10th scale RTR. It really depends on what you are looking to get out of running your RTR. Here is how I rank the current RTR cars on the market
Traxxas Nitro 4-tec - Good for drag racing and wowing friends with straightline speed, not good for racing
Associated Nitro TC3 - Good club track racer, diff gears not able to handle hot modded engines for sanctioned big track races without modification
HPI RS4-3 Evo - Good club track racer, lots of parts available, not good for sanctioned big track racing
Team Magic G4 - Good club track racer, easily upgradable to run sanctioned big track races, can handle hot modded engines.
Kyosho Fazer series - Good club track racer, I believe can be used/upgraded to race sanctioned big track races (don't know a lot about this chassis)
Again, this is my take on the RTR cars that I know are currently available. The main thing is whether or not your local hobby shop supports the vehicle you want to get and if they don't, how easy is it to get parts for it when something breaks. Also, if you do decide to race it, are there racers at your track that run the car that can give you setup tips, etc, to make the car more competitive? These are some of the other factors you need to strongly consider.