My vote goes to the 9mm. I think the "bugs" have been worked out of the 9mm version better. In addition, you get an extra round and with the advent of the very recent premium self defense ammo,* 9mm is not the disadvantage that it once was. Plus, due to the weight of the ammo in the gun, the 9mm version is lighter - a small amount, but noticeable. Also, recoil is more pleasant allowing better use by non-dedicated persons and quicker follow-up shots.
* By premium self-defense ammo, for this purpose, I refer to Winchester RA9T, RA9B (if you expect auto glass barrier) or RA9TA. Those are my favorites, and others swear by their favorites.