A wise old Roman said, “De gustibus non est disputandum” (Latin for "in matters of taste, there can be no disputes").
The French version is “chacun à son gout” (to each his own taste).
In the USA we say “whatever turns you on,” “whatever floats your boat,” “whatever tickles your pickle” and “do your own thing.”
While designing and evaluating book covers it’s important to recognize that there are great variations in personal taste.
[above] I think these two very different book covers are very attractive—but you may hate one or both.
I personally consider the cover at the top to be creepy, disgusting and disturbing—but that may be exactly right for readers of its genre.
Know your customers.
(Adapted from my upcoming The Look of a Book: the difference between good covers and bad covers and how to make a good one)