Doom 1: Favorite: E2M2, cause i love me berserking imps and crate mazes
Least Favorite: E3M5, don't think i need to explain why
Doom 2: Favorite: Map 10, open ended maps are a thing of beauty
Least Favorite: Map 9, mostly for the pointless rooms with the elevators
TNT: Favorite: Map 13, cause on a fundamentals level it's absolutely genius (sequence break at the beginning and computer map right at the end to encourage multiple playthroughs)
Least Favorite: Map 25, just cause you can just skip map 22
Plutonia: Haven't finished it yet, but thus far my favorite map is 4, and i haven't found a level i dislike yet
Edit: wow, i revitalized this post...