I wouldn't use AutoCAD for 3d to save my life. It is quick with snapping though...but mostly 2D.

Maya would be better suited to organic modelling where you can work from a base image or where you have a CAD base to work from.

For basic massing and even some detailing there is nothing that comes close to SketchUp though. It's very fast and VERY intuitive. It's not good with curves though...