I'm not really crazy about any strap on rack, but I think that Saris Bones is the best of the genre'.
It's quite adjustable so it will fit onto ALMOST any car and ALMOST any bike. I like the metal cam lock straps because they are less apt to loosen up en route. Nothing on it rusts. Once you mark the spine with the settings for your car it folds up nice and compact for storage when you're not using it.