I have owned and shot a Glock 21. I lean toward fatter grips, though I have average size hands. The G21 was a great shooting gun. Even with a grip reduction it was just too big in the grip for me.
I now have a XD 45 Service. This gun fits my hand just fine and is a nice shooting gun, too. I've used it a couple of times for IDPA matches and it handles quite nice. Recoil is a problem for me shooting the XD.
I will be giving the M&P45 a shake down at some point. If it shoots as good as it feels in my hand, I'll be buying one.
I was just thinking...just as recoil bothers some people and not others (or has a different effect on their shooting), gun design has differing effects on each of us as well. I like shooting very different guns (M&P, XD, Glock, 1911) and do about as well with all of them. Some folks find a gun brand/model that they like and they do not venture far from it.
Note that I did NOT state that I was any good with ANY of the them!