I believe the shorter the barrel is, theoretically the more accurate it can be as the rifling is stiffer (more turns for a given length). In other words, a 5" barrel might not rifle (spin) the bullet as quickly as a 3.5" barrel. I know this applies to rifles, not sure about handguns...it would depend on the model.
XD-9 subcompacts are very accurate, especially if you have the sights mounted by a very qualified gunsmith (like those at springerprecision). You can also get match-grade barrels and triggers. The 3" XD-9 is super easy to conceal, is lots of fun to shoot, and has a ton of aftermarket options for different match-grade parts. The subcompact comes with an extended grip 16-round mag, which would be plenty big for your paws. Pearce makes finger extensions for the 10-round mags as well. If it were up to me, I'd go with the XD.
I'm not big on shoulder rigs, but some prefer them over IWB/OWB holsters.