I have had both Rancho 9000XLs and Bilsteins 5100s. I ran the Ranchos for about 80,000 miles. Toward the end I new they were bad, but until then they worked fine and I did have the ability to adjust them to the situation.
I decided to try the Bilsteins when I replaced them. My initial feelings were they were great. Did the job of shocks and were a little smoother ride. I have had the Bilsteins for a little over a year and 25-30,000 miles now. The last few months it feels like they are failing some. Starting to feel all the little road bumps harder than I like.
They are around the same cost and I am not sure it is all the shocks fault. I will have the front end checked out soon. I did replace front ball joints and u-joints when I did the shocks so that shouldn't be the reason.
Not sure if this reply helps any at all. :bang