I voted "other", because font size is important, but not in a vacuum. You can have a 9 pt font - if size, kerning and general layout work seamlessly together - be perfectly readable. In general, the D&D-books of the 3e era had not enough white space, too small fonts and not enough variation on their pages. I´m just rereading Red Hand of Doom and it is a perfect example for this. Thank god for 4th edition.