I think the different body style is serving people with different perspective. Obviously the b5 is the most agile of them all, while the b6/b7 has taken the comfort and luxury one step further then the b5 did, but by sacrificing size and weight. With this upcoming B8, I'm sure Audi will find a better balance between performance, and luxury. So my conclusion is,
B5 for performance
B6 for Luxury
B7 is the equilibrium, but still luxury biased
B8 hopefully like b7 but a better performer