to be honest I like the 40x25 bitmap font on MS DOS.

It helps with the O or 0 by putting a slash through the zero, Capital I has lines at the top and bottom, the 1 has lines at the top and the bottom, etc.

Any font that is easily distinguishable like that helps me a ton.

Here is a clone for modern computers http://www.dafont.com/perfect-dos-vga-437.font

(those fonts are freeware but the author accepts donations)