This is difficult. I tend to forget covers and look at the inside of a book. Sometimes I hesitate to buy a book with a cover showing the actors in the latest TV or film adaptation, especially if I read the book before it was adapted.
Most covers seem to date. Possibly a foodie book, like Jennifer McLagan’s Fat – you can see a picture of the cover in the right margin here.
It looks really good with meticulous design on it.