I have both. What I end up using is if it is 2 people +2 bikes day trip, I try to put the bikes with the seats down. If 2-3 people, I usually mount the hitch rack, just easier put the rack on and load the bikes. I use the roof rack only if I have 4+ bikes or using a cargo box.

I could see using the roof rack if you tend to leave the rack over an extended period.
(or I was tall enough to more easily load the bikes on the inside trays.)

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'05 4.4i Toledo Blue