My first hand scientific experience shows that a Glock is more reliable than M&P.
Everything else I got is what I read on INGO and heard from others that are more knowledgable than I am.
I would agree with that, but with a huge caveat. Most examples of both of those guns I see that have problems are not stock. At that point it is hard to blame it on the design or manufacturer. As an example, at a class last weekend, the only pistol that had any problems was a Glock a guy had just put a non stock barrel in and had not shot before class.