The 1911 is flat and easier to conceal compared to the fatter XD. The 1911 has a smaller grip than the XD, which you apparently find more comfortable (as do I). The 1911 potentially has a better trigger than the XD.
Springfield lists the Ultra Compact at 32 ounces, heavy compared to the XD Subcompact at a flyweight 20.5 ounces. Thus the Ultra will be heavier on the belt, but probably recoil less.
The 1911 has a considerably lower bore axis than the XD, making it easier to point on target and giving it less muzzle flip.
The XD holds more BBs. Still, the seven rounds in the 1911 should be more than adequate for any civilian encounter, and 1911 mags are flat and easy to carry as spares.
As far as I'm concerned, the only thing place the XD bests the short 1911 is in reliability. Everything else goes to the 1911, unless a few extra rounds in the gun are a make-or-break for you. And who knows, you might get lucky and get a 100% reliable short 1911.
'Course, I'd rather carry a Glock than either.