If you go to the Mercury Product screens for both of these tools you can gain access to the product sheets which will give the information on each tool by comparing these you will have a good and accurate list of the differences.
Advantages tend to be subjective and what may be an advantage for me may not be an advantage for someone else.
The very basic difference, WR is primarily designed for a Server?Client evironment, QTP for a Web environment.
Surprizingly Mercury says they intend to keep WR for some time to come. The reason they package WR & QTP together is to get QTP exposure by use of the WR scripts to drive QTP. And I thought it was to salvage WR profit. hmmmmm.