No noticeable difference to fuel consumption with our bikes on the towbar rack (Toyota Corolla)
Towbar + fitting and rack cost £260 in total
The faff of putting a bike on the roof for me being 5’4″ is far greater than putting bikes on the tow bar. YMMV
We have a 3 bar rack but only carry 2 bikes most of the time so no juggling required to get them to fit.