I used both on Spridget race cars, and my choice would almost always be a panhard bar, due the lesser amount of sub structure required to mount it, as for the rear end moving about where a third link running between the rear end and the chassis would come in.
Ok with being said, most street car need none of this, they are just subjected to the force a race would be to justify needing this, often time folks look at panhard bars set up when running their tire widths at the max, so they can keep them off the fender when conrnering.
I suggested a panhard bar to David Harrison (Gundy) on his Bugeye, he's running larger than normal tires and wheels for that car and getting a bit of tire rub when hard cornering. Winners Circle,
www.spridget.com , makes nice bolt in panhard bar set up for Spridgets.
In perfect world for performance set up on the rear of Spridget, where I don't abandon what is already there for a coil over set up, I would do a set with rear trailing arms and mount the springs in the bracket (1/2 eliptic car) where they are not pinched by tightening the U bolts, meaning the trailing arms set the rear end, not the leaf spring allowing the spring to be just a spring, and not trailing arm, this would eliminate all spring wrap during hard braking and acceleration, and then add a third link to set pinion angle. Ok with tha being said the tire you can put on your street car, would never allow you achieve the sort of G forces needed to justify this on street car, so a apnhard bar for you guy pushing wide tires, maybe a rear sway bar for you guys pushing it to keep the outside rear wheel/tire form squatting under hard conrnering, other than that, thats about as trick as stret car rear suspension needs to be, anyhting else would be over kill and bling, and nothing needs to be done unless you are really asking alot of the car in the corners, racing or autocrossing or running wide wheels and tires.