I was a Glock hater for years. I didn't like the idea of tupperware in firearms. I still question whether or not the plastic...er...polymer will hold up over time. Seems to be doing well so far, but when I consider old automotive plastic, its obvious that some "polymer" does not age well at all. That being said, I was a huge fan of the Browning Hi Power, 1911 and CZ 75, mainly because of their lack of polymer.
My FFL is an officer who took me shooting and showed me the beauty of the Glock short reset trigger. After that I acquired a G30SF and he upgraded it with a 3.5lb trigger bar. The reset is short, audible and most of all palpable. Their is a very obvious click and absolutely no doubt that the pistol is ready to fire. I eventually ended up with a G23 that I modded and a stock G19 for carry.
I wanted to try another polymer pistol, so I bought an XDM 45. After a couple of range trips, I sold it. The trigger was long and pretty gritty. Reset was mushy compared to the Glock. Seemed top heavy to me with a high bore axis and therefore I couldn't get it to group well.
I bought an M&P to compare to the XDM and the Glock. The M&P feels the best in hand. Its one of those guns that just feels like it was designed for your hand. The trigger however...SUCKED. From the factory the pull was long and the hinged trigger was extremely spongy. Reset was non-existent, but accuracy was excellent, so I decided to try the APEX forward set trigger kit. I installed it in less than an hour. After the install, the pistol was completely transformed! Trigger pull is short, crisp and light. I measured mine at 3.5 pounds. Reset is very short but the click is not near as audible or tactile as the glock, but it is much smoother. The aluminum trigger is wider and fits my finger much better than any other polymer pistol that I've shot. The M&P is so good I briefly considered selling off my Glocks, however, the aftermarket support for Glocks is difficult to match. Availability of M&P 17rd 9mm mags, for example, was extemely limited...if they could be found, people were gouging at a rate of $60 each.
So...to answer your question...if I owned an M&P and didn't own a Glock, I would drop the bucks on the APEX FSS trigger kit. It'll give you a trigger that feels better than any factory Glock trigger, and in my experience, better than the few upgraded triggers that I've used on Glocks. Downside is that in comparison to a $10 Glock drop in 3.5 trigger bar and $10 spring kit, you're paying $165. If you're a tinkerer or WECSOG gunsmith, then the Glock certainly gains more favor for cheaper more readily available aftermarket upgrades.
The biggest difference, to me, and why I like the M&P so much, is because the M&P feels so much better in my hand. But, a downside after messing with it, is that there are little "gotchas" to installing upgrades on it. Notably, to install the Apex FSS, you have to drift the rear sight out to get to the firing pin block...talk about a pain in the ass! They're notoriously tight which is good for the field, but I had to buy a sight tool to get the rear sight out. The Glock internals are much more user friendly to service.
Good luck with your decision!!