A lot of people have said the Dual Core is a lot smoother for day to day phone stuff so if you won't be using the phone for intensive 3D Gaming etc, the number of cores won't really make a difference. I believe Paul O'Brien of Modaco fame actually prefers the S4 Dual Core processor over the Tegra 3 Quad Core and he knows his stuff.
What would swing it for me is the fact you only get 16GB of internal storage in the US version. After you take away the 1.5Gb you lose after formatting, the 2GB space for apps & the 2Gb the ROM takes up, you're left with about a 9GB virtual SD Card. Given the fact you can't add external storage, you're stuck with that 9GB. There is obviously the 25GB you get with dropbox, but I'd find it a pain to copy/delete stuff when I needed space.
Not sure how updates would work either, the US version is AT&T branded so you might have problems getting updates over here. I'm just speculating there though, it might be fine.