I'm pretty satisfied with my iPhone. It has all the functions I need, everyone I work with is familiar with it's software (for collaborations, adding contacts, leaving notes/reminders for me, etc.), and it's good for everyday, popular apps that you might have a need for. The iPhone is generally smaller in size compared to the s3, has more storage space than the s3, and has quicker download/upload times than the s3 which is a big plus for me personally.
Really just depends on what you're looking to use your phone for but that's my view on it.