Horizontal.

To me either way is fine. We have vertical from the entry in our current house. In the house before that it was the opposite. Both look fine.

At first I was thinking just of aesthetics, and for that I like horizontal.

But then I started thinking of cleaning, and I think you would swifter/dustmop/sweep vertically, which might be better for disguising scratches.

It usually depends on which way your floor joists run. If you are on a slab and don't have to worry about that, the rule of thumb is that when you enter the home that you step over the long part of the board (in your case it would run horizontal). My floor joists change in my home and I have some horizontal and some vertical. I must say having both that I prefer the horizontal. The vertical at times can look like a bowling alley.

I find it challenging to walk on vertical floors.

Just a little joke...:-)

Source - https://www.hunker.com/12610437/which-direction-should-wood-floors-run

Horizontal

If you have a room that is narrower than it is long, it can end up feeling closed in. Laying hardwood flooring vertically in this situation would make the illusion even worse. To combat this problem, lay the flooring horizontally. This draws the eye from side to side, instead of down the length of the room. Just like a horizontally-striped shirt can make people look wider than they are, the horizontal stripes created by the floor boards have the same effect on a room.

Vertical

Vertical flooring is the most common orientation for wood floors. If the room is not overly small, floorboards that are placed vertically will work just fine. If the room is wider than it is long, laying the flooring on the vertical will help create the illusion of length in the room and balance it out. The only instance in which a vertical orientation should not be used is the instance above, when the width of the room is very narrow.

Diagonal

Diagonal flooring adds visual interest to a floor and can make the space seem larger. The eye is drawn across the room, creating the illusion of greater width and length. This orientation works very well in tiny rooms where both length and width are an issue. Diagonal flooring can also be used simply to make a floor pattern more interesting or to create a conversation piece for the room.

Herringbone and Parquet are two other options.

Perpendicular to the floor joist otherwise, go lengthwise (horizontal), there will be less waste. Less cuts along a short wall, means you save more money with less waste.