So far as I'm concerned, the two best brands include Clayton and Rubicon Express. Personally, I've been running my RE long arm for nearly five years and it's been problem-free. It isn't the easiest (neither is Clayton's) to install when compared to a short arm suspension kit but it sure is nice once you get it installed. There's a few spots that need to be welded on the RE kit, and I think the Clayton is the same way.
Personally, I'd avoid Tera's and Fabtech's (especially!) long-arm kits if I were installing another. Full-Traction is supposedly good but I'm not all that familiar with it. At least FT got away from using heim joints for everything like they used to.