Italian. As has been mentioned, my experience is also that they have a smoother trigger pull. Also I've had four Italian made guns and put tens of thousands of rounds through them, but I've never had a breech block break, which I've heard reported a lot with the US ones. Slavex said (I think) he had an Italian one break, but I've never encountered anyone in Europe who's had it happen, seems (or seemed, at any rate) to be common in the US though.
I had an argument over many months on the old Compuserve firearm forum with a Beretta USA sales rep over the relative quality of US v. Italian Berettas and many people chimed in with their experiences and it did seem to favour the Italian guns. Which isn't scientific I grant you.
I think the roll marking is done better on the Italian guns too, on the ones I've checked there seems to be less tool marks on the Italian guns. The BUSA rep told me this is impossible because the same engineers came over and put all the tooling in in Maryland, but all I can say is that my experiences have been more positive with the Italian guns than the US ones. I've used a lot of US Berettas at rental ranges over the years, universally they had worse trigger pulls than Italian guns. I suppose you could argue the rental guns get more abuse, not sure how that would make the trigger pull rougher though.
The French MAS ones are better too (well, the trigger pull feels better at any rate), but most of them contain a lot of Italian parts.
Also, the current Italian Berettas have similar "improvements" to the US ones, plastic guide rods, etc.
I think perhaps someone needs to do a "Pepsi challenge".