If you like low resolution sound, the M3 or M50 is the way to go. Otherwise, the M2 is the clear winner.

The M3 and M50 present fuzzier images relative to all other Axioms because they're missing the mid-woofer. Some may prefer this kind of sound.

BTW, I made a typo in the last paragraph of the post just before yours. It was the M2 that was on when my buddy was listening; not the M5.

House of the Rising Sone
Out in the mid or far field
Dedicated mid-woofers are over-rated