Well you're on the Z3 forum, so you're going to get more responses for the Z3.
I've used both, and I kept the Moto X (2014).
Could care less for dust or water proofing. I'm sure it's useful for some people, but for me it does nothing, I have never had phone damage due to dust or water before, and I (alongside several mobile phone owners) have lived a while without this feature.
Z3 has the better battery for sure, but as far as I'm concerned I cannot think of a use case where I will go a full day without having the opportunity to charge my phone. In summary, battery life hasn't been a concern for me, it has never died on me.
Moto X's screen is better in my opinion. AMOLED > IPS but I suppose some prefer brightness over saturation. Personally for me though, no AMOLED = no buy.
Moto X's UI is just cleaner, and there's no arguing that. Moto found a way to put in several useful features in this phone without bastardising the UI. I hate the Xperia UI, and while I realize this is a matter of preference it's what drove me away from Sony. I also wasn't a fan of the glass back of the Z3, I much preferred the wood backing offered by the Moto X (again this boils down to preference).
Anyway, at the end of the day, they're just phones, buy what you enjoy.