AutoCAD is widely used, mostly because it's already present at a lot of places for other reasons, and therefore "free".
From a functional perspective, the bare AutoCAD that's ordinarily used is a horrible choice. Real schematic capture programs allow you to drag devices around and stretch and reroute the lines automatically, automatically generate a net list, understand the difference between inputs, outputs and just plain lines, and can do some simple error checking.
There exists an extra-cost 'AutoCAD Electrical' package from Autodesk. I get the impression that it's okay for generating ladder diagrams. I don't know if it can do schematics.
Mike Halloran
Pembroke Pines, FL, USA