I currently have an S4. I have the Cyber Monday code but I'm torn between the Moto X and Nexus 5. One one hand, the Moto X brings innovation with customization and active notifications. However, i'm concerned about the smaller screen and even less of a usuable area with the on screen buttons. I love my S4's 5 inch 1080p screen.
What has me leaning towards Nexus 5 is the fact that i'm in the last few months of my Sprint contract. Where I live, the service is pretty damn good but i've been wanting to go back to T-Mobile to be on a GSM carrier and can use unlocked devices when I want. I could use the Nexus 5 on Sprint and just carry it over to T-Mo when my contract is up.
I don't have large hands and the ergonomics of the Moto X is another pro.
For me, it comes down to innovaton, customization, and an all-around solid phone vs Stock Android, fast updates, 1080p display and the ability to take it to my next carrier when i'm done with sprint. Hard to choose. My coupon expires on the 11th.