Clayton is the best of those, but it does rob quite a bit of clearance from under the uniframe rails. Too bad they don't make a true front 3-link + panhard kit for the ZJs, like they do for the XJs. Way better than the so-called "3-link" that is actually radius arms with only a single upper on one arm. The rear lowers could use quite a bit more triangulation on the Clayton kit for added side stability and better axle path, but it anyways is a a 4- link without a trackbar (which is a good thing) and as that a much better system than ie. IRO or RE.
Rubicon express is a radius arm front and 4-link + panhard bar rear long arm kit. So is the IRO kit, but IROs single front upper arm thingy is kind of a joke. I would not trust it with a single 10mm/ 3/8" bolt with the weird adjustment system. Rear setup is pretty much the same as RE (4-link + panhard). Installation is a bit more straightforward on the IRO kit.
If I were to choose from those, I'd get the Clayton kit. Even though it does rob some belly clearance, it's the best of those three. With some DIY high- clearance mounts on the belly, it would be even better.
1998 Grand Cherokee 5.9 LX daily driver, 1.75" BB, 32" KM2s, HPD30 Eaton e-locker/D44a stock LSD, 4.56 gears, custom- fabbed tube bumpers and tube fenders,...
1990 XJ Limited (4-door), 4.0 I6, AW4, NP242, ***rolled and totalled @ 165k miles***
1990 XJ (4-door), 4.0 I6, AW4, NP242, PBR 42" tires, Unimog 404 portal axles, 110" WB, full cage + uniframe completely rebuilt, front 3-link + panhard / double triangulated 4-link rear,... ***SOLD***