Floaters are the best, no binding if they are designed properly.
You'd need either a upward facing shackle at the frame (like RIZE or Fabtech...RIZE is better built).
Or a slip joint in the bar itself towards the frame mount like the Daystar/ORU bars.
With either setup...they have to split into two tubes to mount at the axle. One at the bottom of the axle tube (slightly hanging down lower than it) and one towards the top of the axle tube.
Sperical bearing rod ends (more commonly referred to as Heims) give you the most angular movment to prevent binding during suspension travel.
Don't know if there is anything along the lines of a johnny joint that would work in that application.