The LTE Bands. All of them, or as many as I can get. That's my minimum requirement for every phone I buy from here on out.
This Canadian was still with WIND Mobile when he first experienced LTE on a rented mobile hotspot in Japan; after that, nothing less would do. But there was a problem: the Nexus 4 that would go on sale at the end of that year had no LTE support—at least not officially. The Nexus 5 that I purchased in late 2014 came with an LTE radio, but only for the Americas; to this day I've yet to experience LTE data in Hong Kong, my other
favourite Asian tech utopia.
Fortunately our pair of OnePlus Ones support both European and Asian bands of LTE, so using the UK's Everything Everywhere
network in transit to our summer holiday was just like using our phones at home. Which is exactly the way it should be.