I use a stock Kindle Touch for most of my reading. I prefer the sans serif typeface on it because the serif typeface isn't as readable to me. I think that particular serif font lacks weight. This is the opposite of my preferences for most paper books, but the Kindle Touch comes with just serif, sans serif, and condensed as standard typeface choices. I love my KT for the most part but I wish it came with more fonts.
Fonts are important. I have found many paper books that I would have gladly bought except I didn't like how the words looked on the page.