A very difficult one, as I really like most of them a lot.
Seventh Son of a Seventh Son
I like all the references to the past album Eddies, it's very surrealistic and ethereal vibe overall and as a bonus, the inner sleeve artwork is also among their best - if not the best. Scribe Eddie might very well be my all-time favourite.
Powerslave & Somewhere in Time
Oh the grandeur! Powerslave imagery remains effective and outstanding as ever. After getting Seventh Son, my big favourite, out of the way I could have chosen any pair of Maiden album covers from the 1982-1986 era as I really like all of them, but yeah, let's go with these two! They're both rather outstanding album covers and I like the contrast between them a lot.
A Matter of Life and Death
The tank being the centerpiece instead of Eddie is different, but it really underlines the mood, colours and the environment in the art itself. Fits very well with the album and nails the very Maiden-esque balance between dark and broody imagery with comic book aesthetics!
The Book of Souls
Yes, no background, but probably the coolest Eddie since Riggs' 80's heyday. Okay, it greatly benefits from the splendid album book(let) which probably gives a boost to it's "score" as a album cover, but come on... those read eyes, that look... and also, the contrast between this and the previous album cover (especially Eddie) really stood out. And even without all the aspects that (unfairly?) affected this high rating, it's still one of the most outstanding Eddie designs, drawn incredibly well. So there you go... Wilkinson did very well with Senjutsu as well, but The Book of Souls imagery was somehow a perfect match with his style!
Tied with TBOS/not sure?/honorable mention/runner-up:
Brave New World
The borderline between the sky and the cloud Eddie (now when I think of it, The Legend of Zelda: Majora's Mask comes to mind!) and the CGI London landscape is a tad bit too clear, but I really like the colours and the general vibe of it. It's not technically quite as impressive and smooth as my other favourites, but it has some unique charm and somehow, the cloud Eddie, even though it originally comes from a totally different artwork, fits so well and his evil grin, looming over the futuristic London, just works brilliantly.