I like this post because it bring up a valid point. 
What’s important about the covers ?
for me: a reader that had a wide range in his purchases of CoG/Heart’s Choices titles from the “pretty” covers list and also from the “simplest” Hosted games covers one (mostly made not by artists, with mashed up images and photoshoped titles) I find out not always behind a great cover come a great story.
Example: Hosted Game “Scratch” got an unempressive cover but really deep noir mistery story behind it 
. so it remained for me a good surprise that at first wouldn’t pick up with great hopes just for the cover. Same concept could be applied in reverse for CoG titles (not everything that glitter is gold 
) so in a way my suggestion is go with your guts and pick genres you like without prejudices
Is clear having limited funds that the cover choosen for the game make at first a difference in the choice the buyer/reader make in picking up the game… personally I love the covers with cartoonish light tones and are loyal to portray their theme by giving glimpse of the characters in it. For Example: Fool!, The Fog Knows Your Name. Sixth Grade Detective, NOLA is burning. Different genre but the theme is clear even if the cover is less realistic.
For the Mask of the plague Doctor (that I read: A good story) and a Squire’s Tale (still haven’t read it) the covers are more realistic and complex: The first one also give a glimpse of the 3 main characters (the plague doctors) that I find a good touch and I say the dark tone is loyal to the theme of a dark mistery story set in the medieval times so I find them both a good choice as covers 