Best font/size for ebook?

I used to go with Bookman Old style. However, I'm using Tahoma for headings and Verdana 12 pt for text. Repeated feedback from readers informed my decisions.

You had to drag the hamsters into it. I warned you. Now they want a say.

Mr Fullman

It has come to our attention that you have put us in a kettle and used us in a most undignified manner to make your point about fonts. We are not amused.

I'll have you know that us hamsters were reading long before you beastly humans came down out of your trees and started to mess up this fine world. It would seem that hamsters have made much better use of the printed word, using it to further our intelligence and foster harmony throughout hamsterdom, whereas you hairless ones have used the printed word for evil as much as good.

You have also forsaken the serif font in many of your dealings, which can only lead down a slippery slope to total anarchy. We've seen this happen before with undisciplined, immature species such as yours. First it's simply a removal of serifs. Next you remove other things that you find superfluous, but which adds to the beauty of our world.

I weep for your civilization. We shall miss your wheels when you are gone.

Font legibility is more important than serif or sans serif. The concept that sans serif is better for headlines and serif is better for body text is something of an old wive's tale. Usability studies do not bear that out. Legibility is the most important thing. Are the letters clearly distinguishable? Does an "i" look like an "i" and not an "l"?

Take a page from your eBook, and look at it on your screen. Is it legible? Print that same page out on an inkjet printed and look at it. Is it legible? If the answer to both questions is "yes," then use that font.

Note that when looking at your printed copies, make sure the letters really are legible. Inkjets will tend to splatter and bleed a bit, so make sure the "i" doesn't end up looking like an "l". Also, make sure the "e" and "o" don't fill in to the point where they are indistinguishable from one another. If the letters don't print clearly, try a larger point size or a different font.