I looked at all thee of the $500ish polymer pistols that are frequently pitted against each other, the glock, Springfield XD, and the M&P. it is important to fire the pistols before purchasing to ensure a good fit. I was sold on the Glocks simplicity and reliability and then I handled one and could not get a good fit in my hand. The XD was much better, but the M&P fit like a glove. The angle of the grip, it's size (adjustable, I found the medium strap to work the best for me), and it's texture all seemed great and it pointed more naturally to where I wanted to shoot than the glock.
You can't go wrong with ANY of the above three stated pistols, as long as you know what fits you, the shooter.
"They who can give up essential liberty to obtain a little temporary safety deserve neither liberty nor safety." -Benjamin Franklin
The m&p is an excellent gun. I use the large backstrap and it fits like it was made for me! Change to the small backstrap and it's perfect for my wife. Never had any issues with it. It's always performed flawlessly for me. As for the glock... I added a hogue rubber grip to it and that's all it took to make it fit like a glove.