1. Cripplemags suck.
2. Refer to rule #1.
2a. You don't get it. They really suck. . I f****ing hate them. I LOATHE them. I own one pistol that has them, and it's almost one too many. )
3. M+P's in .357 Sig are relatively hard to come by, or so it seems. (I realize I drifted a bit from your question here, so this sort of doesn't count. )
4. Glocks have better holster selection and aftermarket support.
5. Glock parts are FAR easier to come by. If I want a recoil spring I don't have to call the factory, I just go to any store that has a Glock armorer on staff and I get the part. Done.
6. The M+P has no analog to the G19/23, or the 26/27. There is no M+P in the same size/capacity class as these. The compact is too large to compete with the 26/27. All the M+Ps are too fat in the slide to compete with them, as well.
The M+P has better ergonomics, granted, but that's going to depend on the shooter. For some people the M+P will point better, others the Glock will, depending on hand size, etc. I think the M+P will probably suit a wider variety of shooters better than the Glock will.... but I still have no interest in an M+P in anything other than .45 because of all the above.
-Mike