My 73 Charger Rallye 340 CID 4 SPD still has the factory installed K member and torsion bar cross member isolators.

Energy Suspension has them in Polyurethane.
Prothane has them in Urethane.
PST has them in Polygraphite.

I am not considering solid mounts.

I have Polyurethane leaf spring isolators so I am leaning towards Energy Suspension Polyurethane.

I really would appreciate feedback on the 3 options above. I'm looking for the best quality. Cost is of no importance.