Absolutely love it. It's probably the least 'fun' of the M3 and Quadrifoglio in that it can feel a bit too in control, but the way it just grips for days and does the 30-[redacted]mph sprint is addictive. Done a few thousand miles in long drive holidays last year in between lockdowns and it didn't miss a beat; on the motorways it's a placid mile muncher wafting along on air suspension and then when you're really messing around on A roads it'll let you get a bit of slip in the corners without getting too lairy. Up to 33k miles now and the only costs have been fuel and routine servicing with Audi main dealer (last one was £600, interim plus brake fluid), an air con deep clean and regas.
I was told to avoid the 21" rims as they have a habit of deforming on our less than ideal roads. What I have noticed a lot is that because the car is quite wide, you get quite a bit of tug on the wheel on badly cambered roads. It's not unique to the RS6, but it can be a bit unnerving on duff roads. You also realise quite how small so many car parking spaces are. I've also read tales that not being mechanically sympathetic before the engine is properly warmed up can cause premature turbo failures, which could be around £6k to have sorted by Audi, I tend to short shift until up to about 60-70'c oil temp.
Personally, I'd take it out of the three every day of the week because it really can do the extremes of taking your nan to get her supermarket shop and being ASBO-getter, but that's just my cup of tea.
Oh, and dat ass