I worked in a bike shop for years in college and tried almost every configuration.
First, I bought a sweet looking Yakima for the top of my ride. It was a pain to load the bikes (and I'm 6'3") and once up there, I NEVER felt like they were safe. And, Yakima says (at least back then) that you shouldn't drive over 55.
Then, I went with an extended hitch to pass the rear spare, but that thing wobbled around like crazy (again, this was almost 15 years ago, so advances might have been made).
Then, I tried a spare tire hanger, but my non-LC SUV at the time had the spare off center and the bikes sat out too far out over the rear quarter panels.
Eventually, I just started laying down the back seats and throwing the bike in the rear.
I don't know if any of this helps, but I would say stay away from the top and watch for overly "giggly" rear hitch models.
Also, Mr. Bean makes a good point that I missed when I joked about the weight of your bikes (I am a recovering weight weeenie). What types of bikes are you carrying? How many?
Good luck!