Here's my take on a previous post...

MUGEN
EXCELLENT performance
relatively expensive - I agree, but you get what you pay for
EXCELLENT parts availability in my area. Pretty much any REAL hobby shop carries products for Mugen
decent web site support. Its not pretty, but it works

KYOSHO
excellent performance
relatively expensive
parts availability close to non existant, but that should change with Kyosho USA
web site/support - no idea, never seen it

HPI
DECENT - GOOD performance
least expensive - again, you get what you pay for. And just because they've won 2 ROAR championships, doesn't really mean much to me. HARA is an awesome driver who'd win with even a Traxxas 4 tec! (o.k I'm going a little overboard with that one, but you get what I'm trying to say lol)
excellent parts availability - Although, I have heard others complaining about this
excellent support and web site

SERPENT
excellent performance
relatively expensive
haven't seen that great of parts support for this car, although I could be wrong
decent web site - don't know...haven't been on it.

With a Mugen, you can't go wrong. I'd recommend going to a track where people race different brands. I race against RRR's, NTC3's, Serpents, Yokomo's etc...the fastest driver at our track, uses a Mugen MTX3, which is one of the reasons I bought one. Ever since then, I haven't looked back. The MTX3 rides like its on rails. I'm sure the MTX4 will be similar.