Reviews mostly seem to have a hard time choosing one over the other. What I care about:
* Battery life. Reviews are also confused about that, some say the Moto X has longer battery life and some say the Nexus 5.
* Being able to use the unlocked phone internationally (I won't get a locked phone).
* Good, non-jittery GPS that's good enough for navigation/Waze (this is one place the Galaxy Nexus fails very badly)
* Non-laggy app performance
* Easy to read display mainly for maps - but as long as it's not worse than the Galaxy Nexus, I'll like the display.
What I don't care about:
* Rooting. I don't plan to do that.
* Streaming music. I mainly use my iPad to carry music & podcasts around, for the car or for flights. No phone battery is good enough for this use, IMO; iPads last forever.
Edit: Thanks ckd, pir, lizkayl, sariel_t, for bits of helpful info. I ended up choosing Moto X. My main reasons were longer battery life and a smaller more comfortable to hold phone, though I've heard that I'll also really like the "active notifications", and that the camera is much faster.