I'm a happy iPhone 6 user, but every now and then I think about getting an Android phone again to play around with and use as a small tablet. Whenever I consider doing this I can't decide on which phone to buy, and I believe that's a problem for Google and the Android ecosystem.
The iPhone probably isn't the best smartphone at any one thing -there are Android and Windows phones with longer battery life, shaper screens, higher resolution cameras, more features, etc, but it's the best all-around smartphone on the market. If you believe that it's easy to feel good about buying a new iPhone every couple years.
However, there aren't many Android phones that compete so well across so many critical metrics. My Nexus 5 was a great deal, but the camera was slow and inconsistent, battery life fluctuated from mediocre to sub-par, and in the hand it felt like a mid-range phone. Almost any high-end phone from Samsung, Motorola, HTC, etc would have at least one or two major complaints when compared to an iPhone.
There are a lot of great Android phones out there, and the OS enables some very interesting features, but there's no go-to model that's really good or great at everything. I've had four iPhones and have never been disappointed, but I feel any Android phone will disappoint me in some way. After all this hypothetical back and forth I realize I'd probably just be happier with an iPad. Not a good sign for Android OEMs trying to steal share back from Apple.