I've always been told a four link is the way to go. I understand that three links have good articulation, but four links keep the best axle orientation throughout the suspension travel. But then again that would be a double triangulated four link. The full traction kit still uses the stock axle mounts so I guess it's not really a true double triangle.
3 links maintain the exact same axle orientation as a 4 link. Its just that a 4 link will eventually bind, reducing travel compared to a 3 link.
By the way, I dont run either clayton, full traction, RE, or any other off the shelf stuff. I do on the other hand, install, fix, repair, replace, and retro fit all the of the above on a regular basis.
Clayton by far is the highest quality suspension you will find out of all the above options.
What seperates them from the masses is the joints, and bushings they use in there kits. Their bushings alone are worth more then a complete FT or RE cartidge joint. I used to by complete FT cartridge joints to fabricate with for 16$ U.S. a joint. I gave up on them and went back to 55$ curries because they wear out to fast.
Claytons flex joints are currie johnny joints, which are significantly higher quality then RE's and FT's flex joints.
I retro fit a lot of currie joints in place of old FT and RE stuff on a pretty regular basis.
Dont get me wrong, RE and FT stuff isnt "bad" persay. Its just not as good as clayton because of the bushings and joints, which really is the back bone of any suspension.