its cheaper (off contract) and it gets updates quicker than any non Nexus phone. If you buy it through Google, they are pretty good about service and replacements during the one year warranty period too.

The G2 has a slightly better camera and I like that you can wake LG phones by double tapping on the touch screen. The best way to enjoy Android (aside from custom roms) is through a vanilla Android experience. So you gotta go with the N5.

Some other poster mentioned earlier that the Nexus 5 isn't available on Verizon. This is true so if you are on Verizon then go with the G2.

Edit:
The other thing I left out is the G2 does get a bit better battery life due to the larger battery. If you are a heavy user then that is one factor to consider. I don't really have issues with my N5 though since I have it on a wireless charger on my desk at work. Light to moderate users should make it a full day on the Nexus. Anyone who plays Clash of Clans on any phone will never last through an entire day without a charge.