This is a fun poll so we don't have to get into the issue of comparing apples and oranges so here's my list:
2003 RS6 - 9.5
2001 996tt - 10
2002 C4S - 9
2002 Boxster S - 7
1999 996 C2 - 6.5
2001 330xi - 5
2000 328i - 6
1999 Z3 2.8 - 4
2004 A4 3.0 - 6
Personally, I am surprised how much enjoyment the largest and heaviest car I have ever owned is providing me. RS6 is really remarkable.