Well, this is the Moto X forum....
My perspective is that the Moto X is currently the best available Android smartphone on the market for my needs. Do you want:
- A phone with mid-size form factor that can be easily navigated with one hand?
- A little speed demon of a phone?
- All day battery life?
- A near-as-makes-no-difference stock Android experience?
- Additional features such as Active Notifications, Touchless Controls, and Assist?
- A fully customizable exterior?
If yes, buy the Moto with no regrets. The camera used to be the Moto X's big bugaboo, but that's been fixed. It still doesn't have the greatest camera interface, but neither does the Nexus 5 and the Galaxy S4 borders on being too cluttered.
Were I in your position, I'd cross the Galaxy S4 off the list immediately. If the Nexus experience and buying off-contract are more important to you, then the Nexus 5 is a no-brainer.