I am not aware of a Rancho 4" lift spring. Out of all the 4" springs I have run and or had on my brother's two fsj's, I have to say hands down the best have been the Skyjacker full leaf packs. They today are still on my brother's truck and performing great. There have to be 200K miles on them by now.
FWIW, I have heard good things about the BDS ones although I have not seen them in person. Appear to be built a lot like the Skyjacker ones.
'78 Cherokee Chief: 360/TH400/NOS QT, '04 Grand Cherokee: 4.7/545RFE/242HD w/SYE, JK Rubi front axle, 4.56 gears, Protofab rear bumper/tire carrier