Right now, literally all my handguns are M&P's in 9mm and .45.
To be honest, glock v. M&P is basically coke v. pepsi or ford v. chevy. They're both (generally speaking) reliable guns at a reasonable pricepoint with lots of aftermarket support. I think M&P's retail for a bit less than glocks, mag prices are about the same, sight/holster options the same.
The biggest difference is going to be in how you shoot it. A lot of people dislike the grip angle of the glock, not as many people complain about the M&P.
I had glocks in 9mm, then made some moves and decided on the M&P. I like the M&P's ergo's, ability to use holsters I already have for the .45's, and the trigger upgrades. I don't know much about glock aftermarket triggers, but The APEX kits are butter. A guy at the range let me shoot his FSS, Competition kitted trigger and it made me a believer.
They both have their pluses and minuses. Some M&P's come with horrible triggers, some earlier guns had accuracy issues, and some concern about a yr or 2 ago they dropped a newer updated sear housing block. The glock has a pretty decent trigger out of the box, but the sights are craptastic, made of plastic (m$p has steel sights) and some gen 3 and 4 guns will throw brass back into your face (google glock BTF) and I personally had some issues with my g19.
But really, close your eyes, pick one, and rock on.