only problem with the r40 is thta it will have belts if im not mistaken. i dont know about that car but i have the original nitro rs4 and if you dont play in a clean place, you will be going to your car and getting the little rock or pebble that flies up into between your belt and diff gear. it happened to me today, man i hate them.
if u want one just to play around with i would get the rs43. hpi is a pretty good brand. if u want to play around and maybe do a little racing, get the tc3. just my opinions
if you can, try to get a shaft driven car, no worries about those rocks then

but then again, any car you choose you will have a blast with so dont worry