The XD feels clunky and blocky to me. I've fired them (both 9mm and .45) and they work okay for me, just not great. The full size grip is very, very long, and would work great for me if I had 6 fingers on my right hand. It's like a Glock 19 with a Glock 17 grip, seems unbalanced with the shorter barrel and longer grip - and the subcompact seems even more unbalanced, as the grip is waaaaay shorter, and the slide is so tall (not as noticeable in the full size model) that the gun feels really odd to me. Not to mention that the creepily tall slide gives the recoil a lot more moment arm, causing much greater muzzle flip.
The M&P on the other hand, has the perfect sized grip (for my hand). The full size grip is about the size of the G19 grip, lengthwise. No fingers hanging off, no feelings that the six-fingered man should be using this gun to fight off Inigo Montoya. The rounded slide makes the gun look much more pleasing than the squared off glock and XD slides. The gun also conceals far better, both because of the rounded slide and the narrow portion of the slide near the muzzle.
The XD trigger felt, to me, like pressing a paddle or popsicle stick. It works, but I disliked it. I love the trigger on my Glock 19, the short reset really helps rapid accurate fire. The M&P trigger has a bit more takeup than the glock trigger, but the break is a bit more crisp after 400 rounds of breakin (been helping my wife break hers in
). Haven't really looked for the reset yet, but if you're comparing it to the XD trigger, there is no comparison. The trigger is different than the glock, not sure which is better, but it sure wouldn't slow me down if I was considering switching from the glock to the M&P (I was considering - not any more. I'm convinced!)
Then there's the recoil. Glock recoil isn't bad. I'd consider that the standard. Compared to a Hi-Power of the same caliber, it's a bit more. The XD is more like a single action revolver, in that the gun is designed so that the recoil makes the gun twist upwards, or so it feels to me. The bore is just so high above the hand, it's awkward. The M&P has significantly less recoil than either. My wife bought a Glock 27 (.40 subcompact) and the recoil for me was just unpleasant. The slightly smaller and significantly thinner (or it feels that way, anyway) M&P .40 compact has less recoil than the G27, or even the G26. I was quite impressed. The .40 out of that tiny thing was, surprised to say, pleasant. About the same as my full-size all-steel .40 Browning Hi-Power.
I tried to like the XD. I really did. The glock grip angle didn't work for me, and I like single action. So I kept renting one XD after another, trying this guy's XD, and that guy's XD at the range. Then I went back and tried out the glock, and it worked for me. Then I tried my wife's M&P compact, and I am now saving up for an M&P of my own, but the difference between the XD and the M&P is like night and day. I'd say it's better than the glock, but not by as much.
There's my honest opinion, having first hand experience with all of them.