Scott Sheppard at Autodesk has tackled this issue in a very informative post. Is Autodesk DWF file format better than Adobe PDF? In one sentence, if you are only concerned with printing your drawing, then PDF will probably suffice. However, if you want to be able to measure distances to scale, zoom in to view specific drawing areas without losing image quality or maintain the original drawing layers, DWF is for you. OK, that is two sentences, but you get the point. Read Scott’s post here for a more thorough discussion.
He also has created a handy table for a side-by-side comparison of each product. Check it out at this link.