Nexus 6P.
I'm on Google Project Fi and already using a Nexus 6, so I need a Fi-compatible phone ... and I'd really like to know how well the Huawei 6P's radios work - especially compared to the LG 5X, since I had issues with the Nexus 4 and Nexus 5 radios giving me spotty (or worse) performance on T-Mobile inside my house.