How I personally rank them:
Call of the Dead (9/10)
Shangri-La (8/10)
Moon (7.5/10)
Ascension (7/10)
FIVE (6.5/10)
Kino Der Toten (6/10)
Although I don't enjoy BO1 as much as I used to, it's still a really solid game and was a great foundation for what we'd build to with BO2 and 3. There isn't a single bad map in the game, but I also don't think any of them are necessarily top 10 material. The closest for me is CotD which I currently have ranked #13.