I think the easy answer is the 6 series because it's essentially the same kind of car, BUT fewer 8's were sold though and that makes it a more special car. The 6 is a rung down in terms of special-ness I'd say though I'd love to have one (650i 6-speed).
BMW needs to reinvent the 8 perhaps. They were the finest expression of the E34/E32/E36 era styling and still look great. The 850csi is near the top of my list in terms of ultimate awesome BMW's.
2008 BMW 328i manual
2003 X5 4.4i
1972 BMW 2002
2003 Audi TT 225 Coupe