There are many fast ones out today.
TC3
RS4
4Tec
are probably some of the more commonly sold. I went with the TC3 because of the kit options. I built the #2031 kit which is for rear exhaust engines / bumpstart. It is also 4wd and 2 speed tranny. The number of aftermarket parts for the TC3 is huge as well.
The RS4 and 4Tec are strong performers as well. I would never take the steam from their ship.
However, if you want what I consider to be one of the fastest 10th scale machines out, then I would look at a Serpent. Rather pricey, which is what kept me from it, but, a thoroughbred winner as you can see in most of the 'big league' races. The TC3 is the next in line.
If I start to get into on-road heavily then I will more than likely get a Serpent. But for the money, the TC3 was the choice for me. For now anyhow.
Read reviews, see whats appealing to you. Then, go with your Gut!
-Chris