I went from a 4S to an s2 to and iphone 5 and back to the s2. For me I just preferred the 4.3" on the s2, the overly long iphone display felt awkward in use and even though I've had every iphone since launch, I found going back to it after android it felt a little basic, designed for people new to technology but for myself it felt like i was using software with parental controls all over it.
Shocking as I'm the biggest apple fan boy out there and my work colleagues really enjoyed that fact.
I'd give the s3 a go although I'd wait for the black version to come out. Make sure you download swift key 3 though as the standard keyboard is very poor after the iphone one!