Hello metalblaze, cheers
for your first post.
In my opinion, the A4 has the best interior of the three cars. Audi is considered by many to be the market leader for interior design. Of course, some people do think the Audi interiors are boring and ultra conservative -- that is also a reasonable point. Audi does not set out to wow people with design. I have not seen the C class' interior first hand yet, so I cannot comment on the build quality, but IMO it is not a particularly beautiful interior. The BMW is good but is a little bit flimsy in a couple of places.