I've ran, built, and installed both.... Oh yeah, when talking parallel 4 bar, are we talking equal length or unegual length bars???

Equal length, parallel 4 bar is easy, as others have mentioned it frees up room for the exhaust over the top of the differential. With a triangulated 4 bar it takes some careful planning to get everything in place, but it can be done.

As Pat mentioned, triangulated 4 bars often get a bad rap for no adjustability...which is true with the majority of store bought kits. But a bit of fabricating (and properly applied math and geometry) a trianulated 4 bar can also claim "infinite adjustability". Not very meaningul or useful in a street car, but in a drag car it means there is only 1 adjusment position that is correct, and an infinite number of adjustment points that are wrong!!!!!!!

A panhard bar is designed to take your parallel 4 bar (equal or uneaual length arms) and push everything totally out of alignment and bind up every non-heim jointed connection point in the rear suspension!!! If you want to do it right, use a Watt's Linkage and keep things in alignment!!!! A track bar is a bit better, but still leaves the rear end doing the Watusi on every compression and rebound!!!!

"Death Wobble" in a 4 bar only occurs when someone thinks their street car is a drag car and install heim joints instead of bushing for the rod ends....Then neglects the necessary maintenance and lube required on heims and half of the heims are locked up on the thru bolt and the other half are loose, sloppy, and worn out cuz they're a cheap junk heim bought when the builder decided to save money!!!!

So, IMO a triangulated 4 bar is for cruizin', an equal length parallel 4 bar is good for street/strip use, and an unequal length 4 bar is best left for drag use only....