A towbar carrier keeps the bicycle lower, making lifting easier. A roof carrier preserves access to the boot but requires lifting the bicycle higher. Roof models can attach at the frame, fork or wheels; the design needs to suit your particular bicycle.
A roof system starts with crossbars and feet; depending on the car, a specific fitting kit is also needed. Check compatibility by vehicle make, model, year and roof type. The vehicle also determines the permitted load, so carrier specifications alone are insufficient: consult the car manufacturer’s instructions.
Before buying, think through the whole routine: lifting, securing, removing and storing the carrier at home. Ask the retailer to demonstrate these steps with your bicycle. This makes it easier to judge whether the setup will be convenient for regular trips.