My favorite is Sandy Peterson, I find his maps to be the most experimental in The Ultimate Doom, such as E2M2: Containment Area, E2M6: Halls of the Damned and E2M9: Fortress of Mystery, I'm also a fan of Ty Halderman (RIP, legend) and Drake O'Brien for their TNT maps, and the Casali brothers for their Plutonia maps.
@Mr. Hypnos I was surprised to hear that you're Dr. Sleep's son. I knew him from The Master Levels, and liked the way how his Inferno maps are somewhat based on Dante's Inferno; Inferno's (the map series) story is fanfiction-tier writing (I mean, it is fanfiction, I think). Nessus from The Master Levels is my favorite map of his. I hope you're doing well now :]