Most definitely the Galaxy S3 Just a more flexible all round phone! I have actually written a review on it if you're interested. You can find it here
I personally recommend I phone 4s because it looks great and works great than the Samsung Galaxy SIII because it works with android.
I have 4S but my brother have GS3 and they both are great we sometimes switch our phones for a change. My experience says GS3 is better than iOS. However I like iOS too.
Both these smart phones are good at their own place. But if you want style and need big screen than Samsung Galaxy S3 is way better than iPhone 4S. But remember this, iPhone is the best smart phone in this Niche, so what ever you are going to get keep this in mind why you are buying this smart phone, for what purpose.
but some popular androids such as the galaxy s3 and s4 have a faster processor than most apple products.