Vertical is the best for any computing that isn’t games or videos (watching or creating).

Reading and writing is a lot easier when you have narrower columns and most scanning is done up-down – human are much better at scanning mostly up-down with a bit of sideways than a lot of side-to-side with a bit of up-down. This is probably because you can more easily capture an entire sentence with one look, and you don’t have to read every word one-after-the-other, but you can’t capture partial sentences on multiple lines and make sense of that.