The M3 is the better choice IMO over the M22 without a sub because of its non linear frequency response. It will give off the illusion of a more balanced and "fuller" overall sound. The M3 bookshelf is more designed to be a stand alone speaker than the M2 and M22 which work best with a sub. On the other hand in comparison, subjectively, many owners find the M22 without using a subwoofer to sound "thin". This is because the midrange/high is more pronounced relative to the midbass and lower frequencies compared to the M3. With the M3, the midbass is more pronounced than the midrange ( which is recessed) giving off the illusion of that fuller sound.

The M22 without a sub will still be more "accurate" but it might not be as pleasing to listen to without the sub. This is what you will have to find out for yourself.

I’m armed and I’m drinking. You don’t want to listen to advice from me, amigo.

-Max Payne