A long time ago I did some googling (aka `research') on the subject and indeed I found out that using serif for printed documents is non negotiable ; it's supposed (and I agree with that) to let the eyes decrypt words faster and smoother than when reading sans serif. Oddly enough sans serif is easier to decipher on screens. I don't know yet which kind of fonts I should use on my e-reader though.

The web seems to think it's a matter of taste and adequacy nowadays:

http://www.webdesignerdepot.com/2013/03/serif-vs-sans-the-fi...

http://designshack.net/articles/typography/serif-vs-sans-ser...

http://www.fonts.com/content/learning/fontology/level-1/type...