Vertical.
I actual tangled this tile with all the designs going horizontally. When I was finished, and rotated the tile around, I realized that it worked from EVERY position. That‘s unusual, and it gave me a big thrill. I almost didn‘t shade it, just because it was cool! I finally settled on this position, but if you turn your head, you will be able to see what I mean!
Zentangle drawn on Strathmore Bristol Vellum using a black Micron pen.