In an 8' ceilinged room, think about the total number of linear feet of flat seams. There is always less footage if you run the sheets horizontally, especially if you can use 12' sheets. If your walls are longer than 12' you will encounter having to tape the butt joints, but they are only in 4' increments.
You have taller ceilings, so to me it's a PITA to tape the vertical seams in a tall-ceilinged room. You will end up starting and stopping the knife a lot, and leaving uneven mud. Any time I can minimize start and stop it is better. Horizontal seams can be easily taped from a false floor or other staging contrivance; the only way to do the run of vertical seams is with a ladder, and stooping over.
One time, where there was to be a chair rail and the ceiling was 10', I hung 8' sheets trimmed to 7' vertically down from the ceiling, and filled in under the chair rail with horizontal cuts (3' rips) and let the chair rail hide the beltline seam.
Casey

Full sheet up, full sheet down, fill in the strip.
That leave you with a bunch of work 4 feet off the floor, a comfortable height.

Vertical is more common in commercial work with decorated panels that are NOT mudded at all, but us trim strips (often plastic) to cover the joints.

Thanks for the help, both of you. It makes perfect sense now, one up at the top and one down at the bottom and fill in the 1' strip between. Most work done at the 4' level or the middle. Very few ends with 12' pieces

Is your baseboard tall enough to cover a seam at the 6" mark? If so, you could use 54" sheets sideways and only have one tapered seam to tape nicely at the midpoint of the wall.

I would say vertical to reduce the amount of square edge joints unless it is a veneer plaster system (blueboard)

No, it's going to be just a plain old sheet rock system over tongue and grove boards.
I'm in South Texas and I don't believe I've seen plaster in this area. I could be wrong.
So far, it sounds like what is the easiest for you would be the way to go. At least in this case with solid wood walls.