The radio that comes w/ a rtr is usually an AM radio,bottom of the barrel.Companies do this to keep the price down.
If you wanna go all out you can get an arr(almost ready to run)car,then put your choice of radio in it.
An FM is going to be better.Also the higher priced radios have lap counters,end point adjustments,11 model memory,etc.
It all depends on how far you wanna take it,and how much $ you want to spend.
I personally haven't had any problems w/ my stock AM radios.
Regards,
BNZ'