All the differences are very minor, like how the GS3 had the dual-core krait and the quad-core exynos and the two versions didn't differ much performance wise. You'll see slightly better benchmarks and battery on the exynos version, but that's about it. The snapdragon one will have LTE and be far more compatible with apps and games. You will also pay much more for the octa exynos one, which will be rare to find as the majority will be the snapdragon version. Samsung is gonna update the more widespread version first, which is the snapdragon one.