There's no difference in comprehension, reading speed, or preference between serif and sans serif fonts.
People identify letters through pattern recognition. We don't memorize a version of every letter - we know the pattern of what it looks like.
Font choice is not critical to readability as long as it is not so decorative that readers cannot easily recognize the patterns of the letters.
Fonts affect the interpretation of text. In a study, the task was perceived as easier if the instructions were in an easy-to-read font. The task itself was perceived as harder to do if instructions were given in an overly decorative font.