M22 or M3 isn't so much a case of better speaker as it a case of different sounding speaker. As Ben noted the M3 has less midrange giving a a more laid back sound and at the same time it has a slightly depressed lower midrange and a slightly increased upper bass giving it the impression of more bass. This is a good thing if you are without a subwoofer.
The M22 is a very neutral/flat speaker design, very little coloration to the sound and more indicative of the usual neutral Axiom sound however, there are a number of people with M3/VP150 combination and love it. It comes down to personal preferences.
FYI the M22 and VP100/VP150 work very well on a mantle as seen
here.
