i second that for the losi if you do decide to go the RTR path. i dont have much experience with other RTRs, but its a nicely built car and probably wouldnt take much to upgrade it out to the race kit specs.
but if you planned to skip that and go straight back into the big boys, its hard to say which i would pick. it all depends on how much you wanna spend and how easily you can get parts for it. other than that, its a close race IMO. i run a mugen and love it, but i cant say that i wouldnt try something else, they all have their pros and cons..