"Lots of little things I just really didn't like about it. The keyboard is terrible (there's no way to try even one other), the screen is tiny, the appstore is blatantly censored for political views and there's no way to sideload apps, I can't use lockscreen widgets (or widgets at all), can't replace the battery (useful on long trips), can't expand the tiny storage space with an SD card, no Bitcoin allowed, etc etc. Android does everything I want it to, so I switched to it.
App store censoring is annoying, lockscreen widgets are cool, I agree, and replacing the battery and storage is awesome. The downsides just threw me off too much though. I'll probably try the latest and greatest Android offering in another year and a half, when I am again eligible for an upgrade, and see if I like it.
The keyboard is way better on the iPhone though. It actually autocorrects properly. If you do so much as add an extra letter on the S4, it would come up with all sorts of words you didn't want. The iPhone's autocorrect is just a lot smarter, and means I can type essentially without looking and very quickly, and it almost always comes out how I wanted it to, even though every other letter was mistyped.
It's true that the iPhone keyboard is better than the Samsung one - but Swiftkey (a third party app which replaces the Samsung KeyBoard) is WAY superior to both of them. You can actually fully customize it, it learns the way you write and it pretty much "writes all alone by itself". Plus, on Swiftkey you can set up three preferred languages for the autocorrection, so you do not need to switch between languages when writing. I know many english speakers only write in english, but for many of us who use +3 languages per day is a HUGE advantage.
I think you shoud have given a little bit more time to your Android - it's true that iPhone works pretty good "out of the box", while on the contrary you need to tweak the Android for it to really shine. But, as soon as you have put a little amount to work in it (downloading the widgets that are relevant for you, replacing the keyboard and other apps that control key functions), you will discover a world where "everything is possible", while on iOS you are locked inside Apple's very limited world.
For now though, I am quite enjoying the addition of an iPad to my arsenal of electronics, due to the money saved by just using my old iPhone and selling the S4.