After much debating, I decided to start with Hoshido. Originally I was going to play as Nohr, because I like them better, but I decided to save the best for last. I will probably see the Nohrians as evil when I play as Hoshido, but when I finally play as Nohr I'll be able to see their side of the story (literally).
One of the other main reasons I chose Hoshido is because it will be much easier. Why start with the hard one, and then have a cakewalk to follow? I will probably play on hard difficulty, so it will prepare me better if I start with Hoshido.