I recently subjected some figures to an online 'quality analysis' done by a journal I am submitting a paper to. The analysis stated that my figures (created with mpl's pdf backend, and using whatever default fonts are used) used type 3 fonts, and that I should use type 1 whenever possible. I figured Arial would be a safer bet, but that also drew complaints. I have read a little bit online about the difference between types 1 and 3, but I can't find a description of which font is which type. So what font should I use?