I would say V7 or 9 advanced (9 advanced can make vids look fairly comparable to mpeg-2 at a nice reduction in size) . If my memory is right V8 had a few bugs in it. I have not encoded over 50 WMV clips though... If you need a definitive answer, I would visit
www.videohelp.com forums and ask them, though if you need an answer asap that's not going to help you (you can read posts, but can't post for 24 hours I think after activating your free membership). People at Videohelp.com are usually really friendly and are wiling to help you out on just about any video question.
The thing I really dislike the most about the WMVs I?ve encoded that the image has ALWAYS been way too soft looking, I just could never get any crispness using them.