I'm a long time Glock guy but never one of those guys who bought into the "Glock Perfection" BS. They got a lot going for them but are not perfect IMO. So that being the case I've tried all of the "Glock Improved" attempts (XD, M&P, etc.) hoping to find something vastly improved but I have yet to find such a gun.
Now as far as the M&P's go, while I don't find them vastly superior in any way, I do feel they are a comparative equal meaning better in some aspects, not as good in others but overall a viable alternative. When people ask me which one to get, I tell them to try both and then get the one that they like better or shoot better.
The big thing for me that kept me in the Glock camp is, I have a lot of time and money invested in the Glock platform (trigger time, guns, mags, parts, holsters, etc.) and I didn't see any point in setting all of that aside just to switch to a different platform. The trigger was the biggest thing for me, not that the Glock trigger is great but I still think it's better then the M&P (without having to upgrade it). The M&P is a little more ergonomic but it's not a night and day difference for me.
That said I did just get an M&P Shield last night because I'm tired of waiting for Glock to come out with a single stack 9mm. I waited for S&W to come out with a non-manual safety version and then let that one be out for a little bit so they had time to work the bugs out. The one I got has a decent trigger but the reset is still a little long and weak for my liking but then again, I'm comparing it to a Glock which has one of the best reset's out there IMO. An Apex trigger may be in my future?