Because I will inevitably buy both versions (all three, if we get the neutral dlc), I'll probably start with Nohr because Hoshido is the one with the map, where I'll inevitably spend hundreds of hours min/maxing. I'm worried that Nohr's harder difficulty will leave me disappointed when I switch though, so we'll see. Either way, Fire Emblem has instantly achieved what took Pokemon nearly 20 years to do; make me buy multiple versions of the same game. Although I did buy all of the gen 1 and 2 games so I guess they did it right away too.
Here's where I would write something I think is witty at the time, and later realize I'm an ass.