I have a 4" RCD lift and am quite happy with it. For me personally the biggest differences I found was in the radius arm drop brackets. Most of the lift companies just use a pretty simply bracket to drop the radius arms that to me looks pretty cheap. RCD as well as Icon and maybe another place out there use a more beefy drop bracket that appears to have a good beefy design.
I have found, and heard that it is a relatively common problem, that with the track bar drop bracket and drop pitman arm on the RCD can sometimes connect. At full cut and hitting a bump the pitman arm will sometimes rub on the drop bracket. The bracket can be trimmed to fix it, or just make sure you stop turning just before full lock. This has wiped out the seal in the bottom of the steering box but doesn't appear to be anything more.
The springs up front ride great though, nice and soft with a bit of body roll but then stiffens up good for surprisingly good handling, I never thought an 8,000lb truck could corner this good. Also the rear blocks are a one piece design so no stacking and have built in factor style bump stops. The kit also comes with Bilstein 5100's which I would highly recommend for whatever lift you get, even better would be Bilstein 5100's that are specifically valved for your truck (Icon kit comes with these I believe.)
Height wise I would say the RCD 4" measures up a little low compared to others. I have 35" Nitto terra grapplers and when parked next to a truck with stock tires 33" and a 4.5" Icon lift the other truck was about 0.5"-1" taller than mine.
Course a picture is worth a thousand words...
If I were to do it again I would probably go with the 4.5" Icon to get the little bit extra height but I am pretty happy with what I got.