Completely subjective, of course. My choice for best science fiction cover is Upgraded, art by Julie Dillon.
This cover is endlessly fascinating. I especially like how the arm is drawn in break-apart schematic style, only the arm really is breaking apart under the influence of the metal rings. (Or maybe it’s coming together?) The cyborg herself looks very relaxed during this.
Upgraded is an anthology of cyborg short stories. I haven’t read it myself. The stories seemed too avant-garde or new wave or something.
For best fantasy cover, my choice is Night Owls, art by Dan Sipley.
This cover captured the contrast between the two female leads. There’s a great deal of subtlety here, and you can see how claw-like the crouching woman’s nails are.
Night Owls is an interesting New Adult novel about occult forces invading a college campus. Facing off against them is a mismatched group of people who really don’t trust each other, but who will have to work together. Believe it or not, though I liked the plot and characters, I didn’t finish it because I didn’t like the casual swearing in one viewpoint character’s narrative.
Best runner up is Peacemaker, art by Joey Hi-Fi.
You have to give this artist points for being different. This definitely attracted my eye to it on the bookshelf.
Set in the future, the character on the cover is a tough ranger in the world’s largest nature reserve, set on a coast near a megacity in Australia. I did read Peacemaker and enjoyed it. Then I was shocked to see it described as fantasy. I thought of it as science fiction, and the cover reinforces that.
But she does have an animal companion who is invisible to others. So does the hunky U.S. Ranger who barges into her life, whom she resents at first. And she’s attacked by things that don’t show up on recordings. Oh. It’s an urban fantasy, set in the future. So this is the best cross-genre cover.