Just an opinion from a newbie....
I'm only 8 weeks into a new RS4 and it's great. However the RS6 would be a considered choice. I test drove the RS4, RS6, E63, C63 back to back over a weekend.
The RS4, felt the right size for the moment (my small person is 6) but the RS6 will go on order in about 12 months as said small person grows, and for me it was top of the tree for everyday use with decent space. It felt bigger than the RS4 on the road, but more refined, updated and actually an easier drive but more mental when it was time to push on.
The E63 felt a lot bigger...but more refined as a cruiser. And the C63 whilst sounded bloody brilliant it in some ways didn't feel special enough or look special enough.
All rounder, city, country, wet, dry was the RS6. Although you may need to find a slightly bigger parking space.
The other positive was the Mrs was a little bit further away in the RS6 compared to the RS4....so I couldnt hear her telling me to slow down as easily
