Unbiased opinion:
i went from a 3gs to an s2 and couldn't get enough of it, however i'm on my 3rd s2 due to software issues, hardware issues, apps crashing and just generally not working properly. At least the iphone worked properly and the interface is so much nicer to use than androids.
I was impressed at first with android but as time went on I found it just lacked the organisation and fluid motion the iphone has.
As much as i HATE apple, the iphone, although it lacks the spec the s3 has, will still be the more popular phone and to me is a no brainer. Plus the metal back should be a lovely touch.