personally, i've never been a big fan of the hitch mount racks. i hate leaving my bike in the back for some one to hit when they're not paying attention. from what i've seen, the thule and yakama hitch racks look pretty good. they seem well built and the hinges on the part that swings away looks strong. just remember, that more moving parts means more to break though. hitch racks have the advantage that you don't have to climb up on the truck to load your bikes on the roof, but i feel safer with my bikes out of the reach of rear-enders. of course you have to worry about running into the garage with your bikes on the roof. i've used thule roof racks for years and found the construction to be great quality. i'm not a big fan of the plastic thumb screws they use, after a few winters they become brittle and break, but they're easily replaced. i'm not as familiar with yakima, but they appear to be equivalent quality to thule. i would imagine that the hitch racks are built to the same quality standars as the roof racks.
mike