But it's damn hard to play scout for attack/defend in dust bowl, and the game usually ends in seemingly endless stalemate that is eventually broken by BLU. With the exception of Gravel Pit and Steel. But then again Gravel pit and Steel are on their own category.
I would vote either KOTH (specifically viaduct, pro_viaduct or Snakewater or some other map which escapes me), or Payload (specifically Upward, Barnblitz and Swiftwater).
If you have never played these maps before, you are a bloody idiot. I myself was a bloody idiot until I played these maps, and suddenly the game made so much more sense (also fiddle around with screen resolutions. I was an idiot before I fiddled around with screen resolution). Of corse scout is considered one of the most powerful classes. Of course the paranoid heavy/medic pair is not invulnerable. Of course rocket jumping provide soldiers with massive combat advantage.
Honestly though, any maps not Nucleus, Dust Bowl, Harvest, Junction, and Gold Rush is fine with me.