I used to be an iphone user and now i own a samsung s4 there are some nice feature with the samsung phone but what i'm started to realize a lot is the fragmentation. For those who own android that doesn't agree that android os is fragmented you're in full denial. Yes the android does allow you to change the look of your phone but what people don't realize by adding these changes it would suck up a lot of memory which causes your phone to dramatically slow down. It's really no different from Windows it doesn't release memory properly which sometimes causes the phone to crash. I think both iOS and Android OS have their own benefits what it comes down in the end is what's important to you.
a) ability to change the way your phone looks - android yes
b) apps ( personally I think the quality of apple apps are far superior than android)
c) ability to change battery when needed (iphone doesn't)
d) ability to add additional sd memory (apple doesn't however it's never as fast as the main storage)
just my thoughts coming from both side