if you have multiple bikes to transport ... a roof rack is the best option
A towbar-mounted rack is much better. It doesn't create as much drag as a roof-mounted rack and it's much easier to get the bikes on and off - an important consideration if you are advancing in years.
It does require the vehicle to have a towbar, though, which can cost a bit to get fitted if it doesn't have one already. Though to be fair it's probably not that much more expensive than a decent roof rack e.g a Thule or similar, on which bike carriers are then fitted. People spending four-figure sums on a bike shouldn't really have qualms about spending a few hundred to be able to transport it safely and securely by car.