IMO, a properly designed Watts linkage is better than a panhard bar on a road race car.
There isn't any side-to-side motion on a watts linkage through the travel IF the links are the same length and parallel to eachother at ride height.
The advantages of the panhard bar are: Ease of fabrication. Cost (fewer rod-ends). You can easily adjust your roll center by lower/adjusting the mounting locations.
The disadvantage of the panhard bar is the axle will move side-to-side through its' travel. A 40" long bar will move .112" to one side in 3" of travel.
[This message has been edited by Quickshoe (edited January 20, 2003).]