Here are my thoughts.
I currently have an iPhone 6 Plus and a Moto X (2014).
I am very, very interested in the Nexus 6, but I always keep going back to my 6 Plus. The main reason, at least for now, is that 6 Plus makes better use of the larger screen size than Android does. I've used an LG G3, as well. iOS seems to scale better on different sized displays, which is a very nice feature. I can simply see more information on apps that are optimized.
Now, if the Nexus 6 does the same, it would be a killer feature. However, Android apps historically do not scale well. It's why I dumped my Nexus 7 and went with an iPad; having an optimized app ecosystem makes all the difference in the world.
There's a lot to like about the Moto X. Active Display is a great feature, and there are some really compelling features on the phone. The camera, is so-so at best. That will always be Android's weak spot, IMHO. Their camera software, in general, is too aggressive with noise-reduction and processing. I have yet to see a photo experience that rivals that of iOS. I don't think the Nexus 6 will end that either.
It all comes down to personal preference. There's high and low points about each ecosystem. Personally, I always come back to iOS. I like being able to manage and organize everything through iTunes, personally. That's a big plus to me. Apple is closing the gap with web services through iCloud, as well.
We'll see what happens when the Apple Watch comes out, too. Google has a head start with Android Wear, and the gen 2 devices will push out around the same time as the Apple Watch launches.