I have been looking at both myself, and I like them both. The XD fits my hand better. I have shot the XD and shot it well, but I have not had the chance to shoot an M&P yet. The slide on the XD is slightly more narrow, but I don't think that it is enough to make a lot of difference for CCW.
I should also add that the XD usually sells for less and has more stuff with it.
You probably won't go wrong with either.