The American version of the S2 is way too big as a result of Samsung making the screen larger.
I have a friend who generally changes phones every six months, selling them on ebay, getting the new carrier to pick up his ETF, etc. Anyway, this is his passion, and he's an superuser. He's switched back and forth to Android a few times, but always gravitates back to the iPhone because he still believes iOS is a better experience.
That changed with the S2. It's the first phone I've heard this from him, and he's been doing this for years. He said Android has always kinda been a computer, but no phone had the processing power to drive it correctly. Said that's all changed with this phone and he considered it a legitimately better phone than the 4. But the carrier sucks, so he dumped it and went back to the iPhone.