Best option for Ingress on VZW (vs AT&T)?

Hey guys,

I'm looking to pick up an Android device solely for Ingress to add to my current Verizon account. I have to carry an iOS device for work so this is a secondary device; there is pretty much complete freedom on the hardware and no need to think of calling or text needs.

Given the fact that Ingress seems to suck battery down and and pure android seems like the best option, is there a good choice on Verizon or am I better off getting an AT&T device for a straight Nexus option for faster updates? If I go with AT&T, I'd likely go with an older device to avoid a contract since I have a large corporate discounted VZW account and prefer it on there with lots of data. Given that, what device should I look for?

Money isn't really a concern. I'll likely just buy the device outright since if Ingress really takes off, I'll likely just sell whatever I buy right now and upgrade anyway. So for a budget, let's say $200-$800 just to put a number in there.

Thanks for any advice.