I have a few favorite DM maps of my own, but I am curious what the masses out in the ether of the internets consider to be fun, balanced DM maps.
For Doom, It would have to be level 13 (downtown). I probably played that map with my friends from Midway for ages. I think it was so fun because there were great choke points where great battles could start up, and it was fun to control the resources on the map.
In Quake, it would have to be DM4 or DM6. Now that I think about it, it would have to be DM6. I loved the fact that a faster player, using speedy tricks like bunny hopping and rocket jumping could own the map over less experienced players.
In Unreal Tournament, I would probably have to say Phobos. I like the setting of the map, it has a great feel to it, and I think it's just around the right size for a small FFA or one on one match.
All time favorite? 2fort. I can date playing this map all the way back to the original Quakeworld when Teamfortress first came out. I probably did hundreds of clan matches on this sucker, and played it countless times ever since in both TFC and now TF2.