I own both and think they are very good guns. I shot both equally well (8/9/10 ring at 7-10yds). They have gone bang everytime I have pulled the trigger regardless of the crappy or high quality ammo I have in them.
They both have pluses and cons.
I think the XD is better at managing recoil (slightly heavier firearm), has some good safety features (trigger safety and grip safety), it has a nice solid feel to me. Overall, it is shorter then the M&P, but they are the same height and roughly the same thickness
The M&P has better ergonomics, has a higher capacity (15 vs 12), better aftermarket support (trigger kits, etc)
The M&P's trigger does feel gritty when you pull it and it has the annoying take down lever in the magazine well.
The XD is a bit harder to upgrade the sights (they are a PIA to remove from what I have heard).
They are equally good guns with their pluses and minuses. For myself, I give the nod to the M&P due to it feels a little bit better in my hand then the XD.
Best thing for you to do is to test each one and see which one feels the best to you.
I don't have a good signature.....