Not gonna lie. You're gonna get a biased opinion in an iPhone Forum, but I'll try my best to assist you.
I myself, upgraded from an iPhone 4 to a Galaxy S4 at the beginning of this month. Yes, an Admin at a iPhoneForums.net gave the S4 a shot. Well, it took me 3 days to swap the S4 in for a shiny new iPhone 5. Why? I've bought into the iOS and OS X ecosystem and I missed how flawless everything worked together.
Don't get me wrong, the S4 is an awesome device, I just love iCloud, AirPlay, and some other things I missed.
The apps I purchased would've had to have been repurchased again, and that's only if one of the android app stores carried them.
I'm happy with my decision and I can tell my iP5 will give me years of faithful service, as my iP4 did.
Hope that helps.