Samsung Galaxy SIII vs S4

I would like to upgrade from my Samsung Galaxy S (Vibrant I9000M) to either the Samsung Galaxy S III or S 4 - not thinking so much about the price, but more along the lines of "do I really need the S 4"? My ONLY big requirement is a quad band phone for use in N. America and Europe. Suggestions?

via Forums de téléphone cellulaire (en français) http://cellphoneforums.net/fr/samsung-galaxy/t363814-samsung-galaxy-siii-vs-s4.html