I just ditched my iPhone for the Samsung Galaxy S3 during my upgrade two weeks ago. Wanted something new (iOS never changes) and figured what the hell.
Initial impressions of Android software: Wow, you can do a lot of things with it. I'm not one for too much customization, but whatever I feel like changing, I have the option to. The screen on the GS3 if awesome - my wife upgraded to the iPhone 5 and when I use her phone, I know I made the right decision even if based on the screen alone. The only issue I have with the GS3 is battery life. I have searched high and low, made numerous changes to the settings, and it has helped to an extent. With the iPhone, I could go two full days with moderate use before needing a charge. Samsung: at the end of one day I need to plug it in; it even experiences some battery loss when just sitting there in sleep.
Texting is a major hurdle I am still trying to get over with the GS3. I was a fan of the iPhone's autocorrect, it scored a 95% accuracy with me (tried texting the boss "flags" and apple thought I meant "****"). With the GS3, I have to re-read my text just to search for errors when typing - the speak to text option is pretty sweet and very accurate though. All in all, I am very happy with the decision to switch it up.