Look, I see these debates over the M18 and the 18R all the time. What I can tell you, is that when properly setup, both cars run extremely well. The rest is up to personal preference. That being said, if you're talking about racing one of them, it really doesn't matter which car is better than the other if your local area doesn't have a decent turnout with one or the other. In that case, go with what car that can produce the best competition. If you're talking street bashing, than the 18R has better suited ground clearance for that.
As for myself, well I still go with the m18 for pure racing.

Psycho Man