I have both right now. I switch between iOS and Android all the time, so I do not have any blind allegiance. I find Android and really Google Now/OK Google to really being setting Android apart recently. That being said, I tend to like smaller phones (small to me was Nexus 5 type) because I like one-handed use. I generally keep a larger phone for use at work and as a small tablet, etc.
As the person above mentioned, your OS preference would be the first deciding factor. I haven't had the Z3 long enough to say the camera is better, but it is impressive. The Z3 display is better than the iPhone in my opinion (comparing to 6 not 6+). Battery is better on Z3, expandable storage is nice and I feel I can still use the Z3 one-handed. (My biggest concern one-handed is ability to type - not worried about top of screen so much as I keep widgets up there on my Android and use gestures to pull down).
Back to OS - Apps are always a little more polished on iOS because developers have less devices to make them play nice with. As for app availability, it is a wash at this point. iOS 8 has brought some great changes, but still bores me a little. When I need something to just work, I go iPhone, but generally I prefer Android and it's ecosystem these days.
If you have specific questions, I can try and answer those too. What device are you coming from?