Comment by Panzerschrek

Trenchbroom is very good, but I still think, it's not the best possible map editor. It uses brush-based approach, which isn't the right way of designing maps for games in closed spaces (like Quake). Creating each room requires creating at least 6 brushes for its walls/floor/ceiling, which is way to much for such stuff. On the other hand Unreal Editor (for first Unreal and Unreal Tournament) supports creating rooms directly (as subtractive brushes), when two room primitive touch each other, they are automatically connected.