My favourite covers always seem to change the more new ones come out. There’s just so many pretty ones. But being pretty doesn’t necessarily make it a favourite cover. I like covers that are also memorable, that mean something to the story. So right now, my favourite cover for a contemporary book is:
Love and Other Unknown Variables by Shannon Lee Alexander
I like the mostly black and white effect with a little red showing through, the sun in the background, the positioning of the cover models. And I especially love the way math was worked into the title since the main character has such a huge interest in it.