Rick,
I went with the 4" Rancho and have been happy with it.
The installation requires a little cutting and welding, so it is more difficult than most.
The 37's are almost too small for the 4" lift and I am thinking of going slightly larger.
I have photos of my complete install and am working on the technical write-up portion. I'll be glad to let you have all my notes if you decide to do it yourself.
Trav
Travis
http://www.HummerTeam.com