Almost every post on here is saying that you should hold/shoot both and get whichever feels and shoots better. I couldn't agree more. Personally, Glocks don't have a good NPOA for me at all; I end up pointing over my target by 15 degrees. An XDm feels closer to my 1911 when I grip and instinctually aim, so if I had to choose I'd pick the XDm. You may be the opposite so have fun finding out - it's a great excuse to put lead downrange!