my extremely humble opinion is................
Well, I have a M&P .40 and a 3rd generation Glock 22. I like the M&P better because:
the grip is more ergonomic, with 3 different sized inserts to customize it to your hand, and the grip is at an angle that does not make the pistol point high.
You do not have to pull the trigger to disassemble it.
The trigger does not have the ridged safety lever of the Glock that irritates my finger after about 50 rounds at the range.
The barrel completely supports the case. Always that little nagging thought when I'm firing the Glock.
Just like the Glock, the striker assembly is easily removeable for cleaning and inspection.
Metal magazines, not that there's much wrong with the Glock plastic magazines. The magazine drop issue of the early M&P .40's has been resolved.
But I still keep, like , and carry my Glock. Legendary reliability. I 've never had a malfunction with either the M&P or the Glock in .40.
I like the M&P so much in .40 that I've thought about getting a .357 SIG barrel for the Glock and having my 1st 357 SIG.