I'm always amazed when gun enthusiasts start to promote their gun makes/models the same way they promote sports teams ... and seemingly for the same subjective personal (and biased) reasons.
To be fair, though, I suppose if I hadn't been a firearms instructor and armorer for different makes/models for some years, I'd probably be heavily influenced by small samplings & data-sets of personal experience, what I heard at gun stores, 1 or 2 LE agency second-hand tales, etc.
Having worked as an armorer for different makes and models, though, and having seen a pretty wide representation of those and other makes of guns come through years of qual/training ranges ... I'm don't wave flags with the same ardent, unwavering loyalty as some other folks.
As an armorer for both Glock and the M&P pistol series, and as an owner of a few of both lines, I have some likes & dislikes for both. Who wouldn't?
Glock has been working hard to continue to revise their design since they managed to get their toehold in the LE market in the late 80's. The newest Gen4 guns have certainly benefited from continuing revisions, tweaks and improvements.
The M&P, since it's official release at the beginning of '06, and rapidly growing adoption by LE agencies, has also continued to benefited from continual revisions, improvements, parts changes, and so forth. Actually, it's pretty amazing how quickly the engineers have responded to a lot of user feedback in so short a time.
I don't sweat the differences in brands, manufacturing and features as much as some other guys & gals, it seems. I just want the guns to work in the greatest variety of user hands as possible, and have the owners/issued users learn to have the least amount of adverse influence on their weapons as possible (being able to maintain a firearm isn't genetic, it's a learned skill, despite what some folks might wish to believe).
Glock has developed a lot of established marketing since their introduction.
S&W has had to work through the Sigma years, and then look like they weren't "riding the coat-tails" of Walther during the years of their licensed production of the SW99/990L series. (Did you know that there are still at least a small number of LE agencies who haven't transitioned away from the SW99's? I heard they're still maintaining the armorer class for those remaining agencies ... and I rather suspect they've offered to replace any remaining 99's with new M&P's.

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As an armorer for both gun lines I maintain a fair stock of service/repair parts, and I've used them for both. (Ditto for the 99 series, too.)
If they ever make a duty gun that will never require replacement, maintenance or repair parts ... sign me up.
In the meantime? I'll continue to place periodic orders for armorer parts, "raid" factory rep & armorer instructor parts boxes and make calls for unexpected repair parts that aren't frequently needed, but happen when least expected.
Pick what you like, for the reasons you like. Hopefully they're based in some practicality and have been made as the result of an informed choice ... but people can be unpredictable and interesting, to say the least.
If someone feels they really require some degree of external validation about their choice of gun (getting the agreement of other owners, or deliberately denigrating the dissimilar choices of other owners/users) ... maybe they aren't spending enough time on some training/practice range, and working to develop and maintain their mindset, knowledge of the laws, etc.
I have both Glocks and M&P's, as I've said. I've had to service, repair and replace parts in both. Go figure.
I shoot both well, too. It's a training thing.
Suit yourselves.