Which font is easiest on the eyes?
Stick with sans-serif fonts - As mentioned earlier, fonts without serifs, such as Arial, are much easier on the eyes.
Should vertical words go up or down?
So, a good rule-of-thumb might be to favor the human nature option. That is, if the text is to be read ABOVE eye level, then it should run from bottom to top. If the text is to be read BELOW eye level, it should run from top to bottom.