I actually just did the opposite and switched to iOS last week after using android for the past 4 years. I wanted a change, wanted to see what the hype was about. Coming from a galaxy s3 to a 5s. So biaism aside here it goes.
Pros:
Size - it's light...really light and, fits in the pocket well and I can now fully operate my phone one handed! Not saying there arnt smaller phones on the android side, but for my hands I need a 4 inch screen or under for comfortable one handed use, and looking at the android phones in this category none of them are on the level of the 5s spec wise. I always had to go for the bigger phones to get that top of the line hardware/ performance. It feels like a phone...and not a tablet that happens to make calls. I know in most of the bigger android devices they have the one handed operation feature which shrinks the screen down but still doesn't take away from the fact that these things are humongous.
Apps- they are more optimized, usually better designed. From what I can tell they have more support. Since they are in a closed eco system this was to be expected, but it took me a little by surprise just how well they were optimized, it's nice having a VERY smooth experience out of my apps. Haven't had any hitches, slow downs, crashes ect (yet). Android isn't bad either but just isn't this smooth, trust me when I say that. I've had a few hitches here and there with my previous androids where an app would close/freeze or act wonky.
Cons:
iOS biggest pro is also it's biggest con, this thing is CLOSED! and I'm missing my emulators free movies free music.. There's no utorrent on ios, no jailbreak for ios 7 so pretty much what they give you is what you get. Less customization less options...it is like a console and android is like a pc. You can do everything and anything on android.
Keyboard- the google keyboard (download it for your android if you haven't yet) is better than the ios keyboard. Its just more accurate.
conclusion...if one of the android manufacturers prefferably samsung or htc would make a 4 inch phone with 720p and up and a quad core processor I would switch back In a second. But as it stands I'm enjoying the smooth experience and the quality hardware stuffed in this compact package. After all I primarily need this to be a phone, I'm not looking for a tablet. I can live with doing all the other shit like watching movies, playing emus on my boss ass gaming rig.