Glock, Glock, Glock! Simple, Reliable, Consistent, Accurate, Safe (3 internal safety mechanisms).
I, personally, would only carry a Glock for CC self-defense. It is simple to operate in high-stress encounters (consistent trigger pull, no external safety to switch on/off, great 4 gross motor skills). Totally reliable and dependable. No extra gadgets or sticky-outs to catch on things. I have the 19 & 26. Hubby has the 17, 19, & 26. We all have A-Grip wraps on the grips. I have Big Dot sights. Those are the only modifications we have made. Thousands and thousands of rounds through each one - absolutely NO FAILURES TO FIRE/Feeds.
Husband says he's never shot an M&P but hears they have made improvements on them, especially the trigger pull. Others who have used them say they are great pistols. Hubby has gripped the M&P and says the feel is very comfortable but the Glock actually fits better (with no gaps) which would be more stable while actually shooting.