Tried searching but couldn't find much on EDI car rentals

I'm flying into Edinburgh and driving out the following day towards the Highlands. I have National/EE, Hertz Gold and Sixt diamond memberships, but I don't expect those to have any other effect than maybe pricing.

Is there any company that stands out in a positive way? Should I pick up the car at the airport or the city location to have better luck at getting a medium to large SUV?

All I want aside from a reasonably sized car is to avoid another crappy experience, but that seems difficult these days.

TIA for any tips!