I moved from a Droid MAXX to a Nexus 6, and I do find myself missing some things from the Moto/Droid phone, like superior hands-free voice commands, and the larger battery. Moto has added some things since the MAXX that look beneficial as well (motion commands near the screen, custom voice command phrase, etc). The Nexus is nice for getting latest updates and not having carrier bloatware, and being able to use the phone on any carrier I want.
Part of the question is what features to expect in the new Nexus devices this fall. For example, if you're interested in Android's take on VR, then it'd be best to wait for a new Nexus, since the Moto Z isn't Daydream certified, and I don't know if it can become so later on, or what the implications of that are.
Moto Z vs current Nexus - it's a tough call, but I'd lean toward the Moto Z. My main concern is how long they'll provide software updates for the Moto, but the features on the Z are pretty sweet.