From what I have seen at my local track I'd say the ST-RR. They handle way better. The 8T is a good truggy.
Both the Mugen truggy and the ST-RR seem to float effortlessly around the track, a lot of that does have to do with the person holding the TX though.
Engines.... the GRP .21, Picco .21, Jammin .21, the new Trinity ExoTech .21. All of these have been really impressive. Pipe choices depend on the track and engine you choose, but the 2053 pipe is one of my favorites. It's a midrange pipe.
Edit, don't buy the Kyosho unless you have a reliable parts source. It sucks to lose a race because you can't get parts!