While the Xbox One version of Call of Duty: Ghosts has been confirmed by Activision to run at a lower resolution than its PS4 counterpart (720p upscaled vs. 1080p native, respectively), that numerical difference is less meaningful than you might imagine.
The two versions look nearly identical. Viewing the Xbox One release next to the PS4 , I had difficulty telling them apart. It's possible that the PS4 version looked somewhat sharper, but that may have just been my imagination after confirming the hard resolution difference. The next-gen releases of Call of Duty: Ghosts are so close together that gun to my head, I'd have no confidence in being able to discern which version was which — at least, while the two are standing still.