Everyone's printer is different but for my Prusa i3 clone the vertical arrangement gives a much flatter tile and a better top surface.

The vertical print on the left compared to the flat print on the right.
I'm able to print six roof tiles at a time (print time was almost seven hours) and the quality is great at 0.2 resolution.
I tried a floor tile and there is much less curling at the corners and the clips still work great.
The flat print is on the left below and the vertical print is on the right.

