I find this discussion very interesting and have a few more tidbits to add. I was taught that serif was easier to read because if you cover either the upper or lower half of the word the person has more of the letter left to figure out what the letter is. Anything to make the letter easier to identify might make the word easier to identify. Research would be interesting on this.
Material is easier to read with ample white space.
If the words are too cramped it is difficult to identify letters and words. For that reason you never use novelty type for body copy. Go to your word processor and type a row a lower case x's. Now make each one a different font, choose the fancy ones and the basic ones.