The US versions use the dual core Snapdragon, the international versions use the quad core Exynos.
That said, side-by-side tests show that neither one has a clear advantage - the Snapdragon seems to do a lot better on data speed, but the quad core launches faster. It depends on how many cores the particular app is using. (Apps are written to use cores in a specific way - the phone doesn't just use the cores it wants to.)
It's the same with the Snapdragon quad vs, the Exynos Octo. More cores in the CPU doesn't necessarily mean faster operation of the phone.