What one?!
It all depends on how much you are willing to spend. It also has a lot to do with how much skill you have with engines as well as offroad vehicles in general. LAst christmas I got a traxxas nitro sport as my first nitro vehicle. The first thing i noticed at the track was that it was getting its backside ground in. I bought a racing pipe, ball bearings, pro ball diff and slipper clutch and went back. After those mods it would hang with most people, but I wanted to be over the top fast. So I acquired a T-Maxx engine (the same as the nitro sport, just with a bigger carb and enhanced cooling head). I also purchased a boost bottle (waste of money, but it looks cool, lol). With all said I think the traxxas nitro sport/rustler is the best entry level offroad truck.
My friend had one of the infamous T-maxxes and it is no good on the road at all. The nitro sport hangs with the Maxx running around an offroad course, and even stock it kills it in a street/drag situation. Also the Maxx likes to roll over on the street if it is bumped or if it runs into a curb or something. Not to belittle the maxx though, they are one of the best OFF-road trucks out there. But they are just that only for offroad use.
Mark