I've converted various documents (mainly RTF) for the Reader these days, and what I discovered is that generally I prefer the sans serif font
that comes with the Reader rather than its serif font
For you to try out: I've attached two versions of Peter Watts' sci-fi novel Starfish; one comes in serif, the other in sans serif. For both, I picked a font size of 14pt which I find pleasant to read on the Reader in medium scale.
So which font type do you prefer when you read texts on the Reader?
scottcstoness posted a similar poll
which allows you to demo various different embedded PDF fonts on the Reader and vote for them.