There is a back button to the right of the Home button and a Menu button to the left. I don't know what you would have been hitting to go to a different screen. I have had my S3 for about a month and I am enjoying it. I upgraded from a Droid Eris (if any one remembers those). That being said I really like my iPod Touch and iPad. I don't know why people get into such heated debates over android and iPhone.
it's personal preference about an electronic device. If you like the iP5, grab it and run. The guy at the phone store made a good point about getting an android, already having an iPad I can get stuff that only the App Store or android market have exclusively. Maybe you can root your iPhone and put Android OS on it.
enjoy your iP5!