I've had both products (2 5ers) and also prefer the SteadyFast system. I felt like both perform about the same, but SteadyFast was easier to install and is easier to tighten/loosen. With the JT's, I had to add some structural members due the mounting location. But that would not have been the case with the SteadyFast on that same rig.
Now, if you cared about the source at all, keep in mind JT's are a Lippert product and SteadyFast are built in a small shop by a privately held small business.