Here's my honest opinion. For the most part I like Glock. I carry a model 22 as a duty weapon, but only because that's what I'm required to carry. I don't currently own a Glock but in the past I've had a 17, 19, 23 (which I wish I still had), 26, 27 and 36 (which I also wish I still had). All of my Glocks functioned very well and performed flawlessly. I did not care for the 26 or the 27 due to the "pinky pinch" problem I encountered with both of them. My personal favorites, as stated above, were the 23 and 36. I've got small hands and both of these pistols "worked" for me. The dissatisfactions, and I hesitate to use that word, I had with all of my Glocks was the feel of the grip and the small slide release. The grip was not ergonomically friendly for me. It was like holding a small slightly rounded wooden board. I'm left handed and found it cumbersome sometimes to manipulate the slide release which is very close to the frame. I did install an extended slide release on my 36 making it much easier to access. In Glocks favor is the fact they are overall a great pistol and I will most likely own another. You can get just about anything for them anywhere you look.
About a year or so ago I stumbled upon the M&P line while perusing the Glocks at my LGS. I'd read a little about them online and in some of the magazines. Unlike the Sigma line of pistols, I was impressed with the M&P. Construction appeared to be quality, the grip was natural and comfortable in my hand, the backstrap adjustability was a plus and the trigger pull was smooth. Everything simply felt better than the Glock. I found the trigger, slide realease and magazine release to be easier to manipulate than those of the Glock. I personally preferred the cantilever trigger of the M&P over the safe action trigger of the Glock. I purchased the 40C and enjoyed shooting it much better than my previously owned Glock 23. I've since added the 9C and 45C to my collection. All have functioned and performed flawlessly.
Both the Glock and M&P are reliable quality firearms and you can't go wrong with either of them. It simply boils down to personal preference.
My Opinion