I find the SGS2 feels like a cheap piece of plastic. When I tried my friends one that's the impression i got. It had a decent interface though. My workmates Nexus is pretty cool but. I still prefer iOS.
The 4S looks sexy due to its glass front and rear cover. It might look good but let me tell you, it's not great when it hits the deck, it shatters quite easily. Another way in which Apple makes some quick and easy dough I guess.
The iOS is probably slightly more refined because it's specifically designed for the hardware on the phone, but it really desperately falls short when it comes to features and customisation.
The freedom an Android gives you is really second to none, you can even use the memory on your phone like a USB memory stick. But it really comes down to horses for courses, some people think nothing of customisation options and freedom when it comes to a phone. Some just want a smart phone that can get them onto the Internet.