I've no idea why BA use Avis.

More often than not their actual site is off airport premises and you have to wait for all avis customers to disembark, collect their luggage and get a bus to the depot - infuriating when you are on a schedule and have hand luggage only.

I do my research and use a decent name sited in the arrivals hall and it's rarely avis.

As far as the add-ons are concerned they are all the same.