Make sure the hitch price does NOT include trailer wiring (my UHaul hitch on my Jetta was $160). I had to explain to the guy that I was buying the hitch for a bike rack, who in their right mind would tow with a Jetta, etc., and he quickly realized that I had two good points. I would also point out the damage risks when roof mounting: you have fork ends near your car's paint/sunroof, you have a valuable bike in a position to meet with garages, and you have a valuable bike eating bugs and other airborne objects at speeds well above what you ride. Think about the paint job on the bike and how it'll look after some long drives.

All that said, I have a Thule T2 rack for the Jetta (1.25" mount), a Thule T2 rack for the Excursion (2" mount, four-bike version), and a four-bike Thule roof rack for the Excursion (on the rare occasion that I haul a group). I haven't seen a rack I'd rather have. Admittedly, with a $17k tandem now as our primary ride, all of the racks sit idle and the tandem gets to ride inside the Excursion (sacrificing a seat, but oh well).