> Definitely nothing serif.
I definitely recommend something serif! Sans serif fonts do look great on computer screens, but for small printed text, serifed fonts are the best. At small sizes, the serifs provide hooks for our eyes, making them easy to read. That's why newspapers and most novels use serifed fonts. Quote:
"In his book Cashvertising, Drew Eric Whitman cites a 1986 study of fonts (printed on paper) that found only 12 percent of participants effectively comprehended a paragraph set in sans-serif type versus 67 percent who were given a version set in serif typeface.
Those who read the sans-serif version said they had a tough time reading the text and "continually had to backtrack to regain comprehension."
In a test of three different fonts, two serifs (Garamond and Times New Roman) and one sans serif (Helvetica), he found 66 percent were able to comprehend Garamond; 31.5 percent Times New Roman, and 12.5 percent Helvetica (out of a total of 1,010,000 people surveyed). (source: http://www.awaionline.com/2011/10/the-best-fonts-to-use-in-print-online-and-email/)"
That's just one source, but if you do a little research you will find that printers agree: serif is the most readable for print. Of course, there is a lot of JSIS art in the DQN short novel, so I would suggest using Mona for those sections and a serifed font like Garamond for the rest.
Also watch out for column widths. A common mistake is having columns too wide to be readable. You generally only want seven to eleven words per line (source: http://www.bergsland.org/2012/05/typography/column-width-the-key-to-comfortable-reading/) If you're planning on printing on A4 paper, you might consider printing two columns per page (landscape) to make it fit nicely.
Good luck! Book printing is complicated! What looks good as a PDF e-book won't look as good in print, and vice versa, so you either have to make some compromises or make two different versions.