Strictly speaking from a window-covering point of view, both horizontal and vertical blinds will do the job admirably so you can pick one or the other and be done with it. But who are we kidding? It’s in our nature to tweak the environment to our liking. If there’s any way to optimise our surroundings, we’d be there sure as dust on blinds to seize it. So although blinds will cover windows just as well one direction or another, there are functional differences between horizontal and vertical blinds worth considering that will better suit your situation.