There are a number of reasons to choose a hitch rack over a trunk or roof rack. First, other than touching the hitch receiver, the rack itself doesn’t make contact with your vehicle (unless used incorrectly). Trunk racks can cause damage to your vehicle’s paint while roof racks need to be attached to your factory roof bars or require aftermarket bars attached to the vehicle.
Hitch racks also have a low loading height and simpler loading process that makes them more user-friendly. For tray racks, you only need to lift the bike wheels as high as the tray. Roof racks require you to lift your bike to the height of the roof and loading them can be awkward. Trunk racks require you to lift the bikes to the height of the support arms.
Hitch racks are versatile in terms of bike fit, and most can handle a wide variety of wheel sizes, tire widths, frame shapes, and wheelbase lengths. Hitch racks are better for your bikes as they typically keep them from contacting one another or your vehicle when in transit. You also won’t run the risk of accidentally driving into the garage with your bike on the roof of your vehicle and potentially damaging your bike, vehicle, and home all at the same time.