Well, here's the thing .... the iphone 4S brought siri to the world .... except here in Oz, it doesn't work due to our weird accents .. apparently.
So on hardware alone, apart from the high pixel density of the iphone 4/4S (which the vast majority of people cannot distinguish anyway), the iphone 4/4S is inferior, or on par, in practically every way.
In terms of software, it's basically on par with Android for anyone whom is willing to venture outside the gaol gates. The interface is a little smoother for iOS, because they only have their own hardware to deal with for tweaking.
It's not really fair to compare the iphone 4S with Galaxy S3 directly, the S3 is brand spanking new, and the i4S is about 8 months old.
That said, the comparison is valid because anyone looking to buy cell phones right now needs to know, and the GS3 is the hands down winner atm.