Many years ago when Beretta USA first got started making M9 pistols, the Italian guns looked a little prettier in that they still had a blued finish vs. the black finish of the M9. As time has rolled on, the Italian guns now use the same finishes as the US guns and looking at them side by side it's nearly impossible to tell them apart without looking at the markings.
Some folks think the Italian guns will have a higher resale value down the road, and that may be true. But from a functional and quality standpoint, the Beretta USA pistols in my experience are every bit as good as the Italian made guns and perhaps even better. The M9 is made on some of the most modern manufacturing equipment out there. Thanks to 26+ years of military use and military feedback the M9 has become a very refined pistol.
There was a time when I personally preferred the Italian guns, but that time has passed and I'm quite content with my M9 and M9A1 pistols compared to my Italian 92's.