I owned every model of iphone ever made then switched to a Galaxy S3 and a Note 2,,,and I will be buying the S4 on day one.
The iPhones are really great phones, especially the 5,,,, but after a short time with the S4 your going to discover how much Apple has fallen back in the last few years,,, it's really a bit sad these days to compare the ip5 to the Note 2, GS3 and the upcoming S4.
It takes a small very easy bit of adjustment going from iOS to Android, but after you make the adjustment and get comfortable with Android picking up and playing with an iphone feels like very limited ancient technology.
Anyhow,, don't worry about the switch to Android,,, it's very painless.
Cheers
Davyo