Few key differences between the two lifts. Some are:
Spacer Lift (RL, RC, etc.):
+ Relatively cheap $ vs. full suspension $$$
+ Easier for the DIY (no strut disassembly)
+ Potentially retain OEM ride quality
+ Can be compatible with "smart" OEM struts (such as CCD)
+ Quick results
- Moves suspension geometry out of design scope (CV angles, UCA/LCA BJ angles, etc).
- Items have potential to wear out quicker due to out of scope specs or have clearance issues (UCA contacting springs)
- Can stiffen ride, particularly on road
- Not as suitable for off-roading or aggressive driving
Suspension Lift (Bilstein, ICON, King, RC)
+ Usually higher quality equipment
+ Struts are designed to work within the tolerances of the OEM geometry. Most lifting is in the springs (some add'l length in struts).
+ Generally can be adjusted to account for changes to vehicle weight (bumpers, gear, etc.)
+ Equipment generally will last longer (cheaper in long run?)
+ Can be driven harder off-road/more aggressively
- Generally cost more. Pricing can vary a lot on brand (i.e. - Bilstein vs. King/ICON)
- Some kits require more frequent rebuilds due their design (King/ICON). This can be viewed by some as either good or bad.
- Some kits eliminate bushings which can lead to noisier and stiffer ride.
Either lift can use aftermarket UCA's to compensate for angles and alignment issues. UCA's are interchangeable with same gen F-150, so a broad market available.
This is a good artical:
Pros and Cons of Strut Spacers There are pros and cons to each option, the biggest factor for people going with a spacer is perceived cost vs a new set of struts that may do the same. Spacers are also very popular amongst new truck owners who just want to level the vehicle without replacing...
www.shocksurplus.com
I already have Bilstein 5100's installed in the rear of my truck due to OEM shocks giving out a few months back. I installed at 0" lift and feedback from the backseat is that they ride great, actually better than the originals. I also wonder if going from HD to Billies is more apples-to-apples than non-HD as I did find PN's are different across the board for shocks and springs when doing the install.
I hope to revamp my setup in the next week with front F-150 Bilstein's that I have along with JBA UCA's and SPC Raptor LCA cam kit to go with it. Looking for a ~2"/1.5" lift setup at the moment and it should ride good without wearing out components.