In short, it's a very personal preference. The M2s and M22s are more linear than the M3s. Some people prefer less linear. I've heard M3s, M22s, M50s (own), M60s, and M80s (own). I prefer the M80s and M3s. Of course, I never heard the M3s directly compared to the M22s, and I've never heard the M2s at all. Generally, the Axiom line is said to be split into two: M3s and M50s and M2s, M22s, M60s, and M80s. The M80s and M3s (and M50s) certainly had different characteristics, but the M3s are really fantastic speakers.
That said, when I first heard M22s, it was (a tad hyperbolic here) a revelation. Amazing speakers.
