I've installed 2 SPL and one poly diff bushings so far. The solid diff bushings were easier to install. You won't notice too much NVH difference with the diff bushing. I installed the SPL sub frame bushings. You have to drop the sub frame to do it. you will pick up a little more NVH with the sub frame bushings.
The Complete SPL Rear Suspension (Almost)
SPL Rear Sub-Frame Bushings