bnickel
Founding Member
no one has asked what you're planning on doing with the car?
hard street driving? - panhard
autocross/roadrace? - panhard or watts (there are benefits to both)
benefit of the panhard bar is you can adjust your rear roll center after it's installed (with an adjustable mount). with a watts, once you install it, you can't change the roll center. watts does work slightly better at it's job of locating the axle, but for a serious car that's lowered and on stiff springs, the difference is marginal.
best handling live axle car I've driven (fully autocross prepped '69 camaro) had a panhard bar. that said, my '79 camaro (also fully prepped) has a watts, but I bought the car that way... both cars are 3 link setups.
both of the watts' on the market now, Fays2 and EVM, are roll center adjustable while most of the panhard bars right now aren't, at least the ones that come with many of the 4 link rear suspension at the moment. the Maier PHB is adjustable but you still have the problem of the leaf springs and teh PHB having different roll center heights in most cases, however the Martz chassis piece that comes with their rear 4 link looks to be an atypical PHB setup and if used with leaf springs looks to have about the same roll center height as the springs.