Grab

Because it takes like at least 25 mouse clicks and drags in each perspective to position each brush how you want it. It takes hours to create anything substantial either.

Just block out the level in Radiant, but make detailed models in a 3D package such as 3ds Max or Blender.

Radiant is simple to navigate in and you can build very efficiently and fast with it.

It doesn't make small, round pipes very well but other than that its great.