There really is no choice, you do what is needed for the task at hand, PDF if it's needed, DWF if it works.
However, many AutoCAD/LT users see this as a single-view choice, not grasping, or perhaps fearing, the true power of DWF over PDF.
How about a free viewer that will allow a user to electronically comment on and/or measure content in those files and return to the file originator for an update? Yes, your file recipient, aka the Client, can receive your drawing(s), review it, redline it, and send it back to you to make those important changes.
No, we are not talking about DWG files, or PDF, we are talking DWF. All they need is http://www.autodesk.com/designreview, which is free, and all you need is LT2008 and higher, you can Xref their DWF back into your file and pick up the markups in your DWG file.
But they already have a PDF viewer installed you say, and they fear installing a new program? They don't wish to redline, just look at a file and comment in other methods? Or just look at progress sets? There is a free online viewer, a webpage they can go to, click on the browse button, and open your DWF file with (they can even use their PDA or web-capable phone to do this), click HERE or share that link with them when you send the DWF file.
For the "cutting edge" version of the above, click HERE.
Communication is a powerful business tool, clients respond to it if you bring it up as more than 'just another software package' to try. Give them the power to review on the go, without leaving their PCs or mobiel devices, you do the same.