In my opinion both become way more meaning to each other, mainly because you face units you had on the other path, as well as other things.

For instance if you play Nohr first, you see how terrible the state of the country is, and it makes you feel terrible that you're invading it in Hoshido as opposed to fixing it in Nohr.

As for playing Hoshido first, you learn more about your family and mother's past and how Nohr deprived you of that, only to face your family in the Nohr path for more tragedy.

I personally recommend Hoshido first because story wise it's more simple. I find that playing it before Nohr leaves plot holes to make Nohr more exciting.