Geez, this thread is just as bad as the ones where people insist the only reason anyone cared about the old Tomb Raider games was the boobs. I like Doom, but Duke Nukem 3D blows away both Doom and Doom 2. It's got better level design, more varied gameplay, more interesting weapons, more interesting characters (or enemies, at any rate), and a sense of humor to boot. All modern level designers should be forced to study Duke 3D and Dark Forces to see how it's done. Both games avoided being pointless mazes (which is something Doom had problems with) while also avoiding the modern problem where the whole game is just one long corridor, where if there's ever a branch at all, you know one path takes you to an item, and the other to the end of the level. So yeah, you may not /always/ be able to bet on the Duke, but I'd take his best outing over Doomguy's.
Edit: And then I clicked on the wrong option in the poll and voted for Doom, like an idiot. I wish this forum had a way to change your vote on something.