I was in your same position a few weeks ago. I went with the Glock 17. Here's what made up my mind...
Glock:
- felt better in my hand (the square shape I found gave me better control of the gun)
- pointed more naturally for me
- I preferred the trigger feel and shape over the M&P's (you can lighten the Glock trigger as well by simply buying a 3.5lb trigger connector and swapping it out with the factory connector... there are a handful of companies that make them including Glock)
- parts are cheap, plentiful and easy to find
- mags are $35 ( and you can get 17 round mags pinned to 10 which are way easier to load than the 10 rounders) vs $50 for M&P mags
- tons of after market parts available as well (extended magazine releases, extended slide releases, different springs for trigger pull and recoil management, etc, etc)
- proven track record (20 years or so, and the gun as well as the mags has gone through numerous design revisions, there are tons of Glocks out there with ridiculously high round counts through them still going strong)
- glock torture tests (look on youtube, dropped out of a plane at 500feet i think it was, buried in a bucket of sand, mashed in a muddy creekbed, dragged behind a truck, shot underwater... and they still work perfectly)
- superb reliability (they seem to eat any kind of ammo)
- no gunsmithing required, any part change you can do yourself as long as you have common sense
- excellent customer service
- I personally think they are one of the coolest looking handguns (some think they are damn ugly, I personally have no need for a shiny, pretty pistol with an engraving of a hunting dog with a bird in it's mouth running through a meadow on the side of my gun... YMMV lol)
I am sure there are other things I am forgetting.
My feeling was that the M&P just didn't have the track record behind it, and if you go on the mp-pistol forum (or even here on CGN), you will see that there have been a fair amount of growing pains (some rust problems that werent only isolated to one batch, abnormal wear, FTE, FTF, broken strikers, issues with mags dropping out randomly, etc etc). From what I have read Glocks had some growing pains too, but they seem to have worked them out a long time ago. Kabooms can happen with nearly all handguns (if not all), it is not isolated to Glocks. If you look on the net you will find that revolvers, HK's, Sigs, and 1911's all kaboom. You hear about Glocks more because there are gazillions of them out there (how many LE departments in North America use G22s? LOTS!).
The bottom line for me was that I just didn't want to do S&W's product testing for them, with my hard earned money. I could only afford one handgun right now, and I wanted it to be a proven design, so I could spend my time shooting it.
Good luck with your decision!!