Well, my boyfriend has Galaxy SIII and I have iPhone 5.
Galaxy has bigger screen, so as Beyonceist mentioned, its better when you want to play games. Also Galaxy has Pop Up Play, which means you can view two websites or apps at the same time (you cant do this with iPhone and I really miss this feature). iPhone is a bit faster and smoother than Galaxy. Galaxy overheats sometimes, especially when you are playing games for a longer time and then it freezes, so you have to shut it and wait untill its cool again.
But both are equally great phones and I think you will love your new iPhone just as much as your new Galaxy... I couldnt decide which one to get too, iPhone won just because I have small hands, so its more comfortable for me to use iPhone than Galaxy
