I agree with OTHGWayne, Autodesk now has a great & free DWG viewer for download called Trueview that allows you to view DWG & DXF files (both 2D and 3D). The software also allows you to convert between different versions of DWG files from version 12 to version 2008.
Autodesk also has another free viewer called "design review" that allows you to view, print, measure, and mark-up DWG drawings.
I like PDF better than DWF becasue almost everyone already has software to view PDF files on their computers. Also, the newer Adobe 3D software allows you to animate drawings in 3D, which works great for making 3D presentations, watching assembly parts explode & then implode, etc.. If Autodesk had features like this for DWF, that would be great.