Have you considered just waiting for what you really want then?If I could find one in 45acp, we wouldn't be having this conversation because I would already own one
Of the 2 you've put forth though, the M&P.
The Glock has a better trigger but other than that the M&P is more ergonomic, as reliable in my experience and (IMO of course) comes with better sights and mitigates recoil better.