I have a nexus 5 and now an iPhone 6+. Both operating systems are great for what ever you want in a phone imo.
I went back to iPhone after many years with android because I liked the way iPhones , macs and iPads are now truly multiple platform , you do something in one device and you can pick up were you left off on the other without really thinking about it, I would also say apps are more beatiful and rich on the iOS platform and don't bog down the system .its a phase I used to hate but everything does just seem to work on the iPhone, you get what you get and performance doesn't really go down .
I still have and use and love my nexus 5 though and the new operating system looks beautiful , one thing I miss is the applications draw because for me in iOS having all the apps on the Home screens just looks cluttered and not really beautiful. I also miss Google now because it's far better than Siri in the way it perfoms and integrates with your life.
One problem I did have with android and its to do with the biggest difference between iOS and android , is the fact some apps I downloaded on android effected the performance in the device due to much more access to the system. And it was hard to find the apps that did effect performance. However those differences made some apps far surprise to iOS counterparts.
Either way it's great having this much competition.
I do love the new iPhones though , Touch ID and hopefully when Apple pay takes off in Australia , well it will make it a lot harder for me to go back to android full time . I know Google has had wallet for years but I could never use it like most people in the world , and the fact you have Touch ID working in conjunction with it , will make the functionality and the each of use and the safety of use much better than anything before.
The new android though does looks stunning though I must admit , even more stunning than iOS due to the clutter you get when you have many apps on your home screen of an iOS device because it ends up being a huge multicoloured app mess or screens filled with folders. As appose to your most used apps on your home screen customised to how you want it , then all the rest in the app draw ready to be accessed.