I have developed some ninja workflows on my s3 thanks to a few apps.
Here's some of the things I'd most miss if i switched to iphone, in no particular order
Removable battery so I can charge a spare one and then swap them
Calendar snooze, really useful if your in the middle of something but a critical event is approaching
Email me pro
Email to self
Swiftkey, suggested words are a really fast way to type
Voicenote by Craig Hamilton
Long press paste, just a tad quicker than iOS paste
Be interested to hear other people's reasons, and also vice versa if you use iPhone ...