I've tried a lot
of different fonts on my Paperwhite since I found out how to use the USE_ALT_FONTS about a month ago. Based on how I keep returning to it, I think I've settled on an edited version of Lusitana
at 12 points.
I've poked at it a lot--but mainly I condensed it, replaced the quotation marks and apostrophes with glyphs from another font (personal preference), and used letters from a more decorative font for italic characters (I wasn't satisfied with the auto-italic).
I like it. Regardless, I'm so glad we can tweak our fonts! I hated being locked into a few font choices on my previous e-reader. Having 12 of my own choosing is much better