Good evening.

I think I'm just about to become an Audi owner and seek initially to gain understanding from the knowledge of existing owners, that may help me decide.

Hence for now my profile states as model Ax and year 20xx

I'm looking at A6 ( including Avant and AllRoad )and A8

There's a particular angle to my requirements and thinking in that it will be in use as a taxi. Therefore there might be some things that are intended by Audi to be good but which may not in taxi terms be a good idea, which is one of the things I'd seek to get a better idea about from your combined experience.

I am a cat.

Welcome to the forum, you'll find the members on here are a friendly and helpful bunch. 

If you have an a8 you'll be a very popular taxi driver. We had a member with an a8 D3 w12 as a taxi and he said people would ask for him because of the car when they rang up the firm he worked for.