Despite being a ZR owner, I think Moto X is obviously the right choice for you.
Moto X over ZR:
- Much better support : Motorola, even now sold to Lenovo, is way better to Sony in software updates. Moto X has been always among the first phones updated to new Android versions until now and will very likely get Android L, while the same can't be told about ZR. Also as you can see, there are a lot of custom roms and kernels for Moto X, while ZR is listed in low activity devices section of Xda not without reason. I can't even find a custom kernel with dt2w for ZR.
- Much better camera performance dim light conditions. Sony phones are notorious for blurry pics. In good light conditions ZR camera is good, but I'm not sure if it's superior than Moto X. Also 2M vs. 0.3M front camera.
- Amoled vs TFT display : better contrast and outdoor visibility.
- Cool features : Active Display, Touchless Control, Always on voice recognition
ZR over Moto X:
- Better battery
- Good proprietary apps : Walkman, Album, Social Camera are the ones I miss the most when switch to custom roms
Everything else, imo, are quite similar in the two phones. Well some will cite waterproof as a critical strong point of ZR, buy actually you can't use it in sea water because salt will damage the phone, you can't use it in pool neither unless you want chemicals attack it. When they say waterproof, they mean Pure Water. About some water drops like rain, actually Moto X can handle them well just like ZR (its inside is coated with water-resistant coating). Performance are quite the same.
So why didn't I buy a Moto X
Because in my country it asks $500 while ZR only $300. And ZR is a very good phone in its own right.