If I were in the market for a new ride and had the pockets, I'd go Mugen with a JX Ninja 21... I run AE stuff and haven't had a Mugen yet, but they have such a killer rep, especially for part-quality and durability. It'll be my next brand. I've been evolving upwards I think - started with HPI, then Losi, then AE, next Mugen... X-ray is supposed to be great too, but I would worry about part availability and cost.

RB's are simply overpriced IMO. Especially parts.. If I were to go big money on an engine, it'd be the Ninja. Just seen too many running like banshees, and yeah, they have a great rep as well.