As a former BMW M5 and 7-Series owner I have to say that the Audi S8 tops them both. The S8 delivers the comfort of the 7-Series with the all-out performance of the M5 (but without the cramped cabin). The ride is stff but not harsh and the lightness of the aluminum body and suspension makes it feel like a much smaller car than it is. Nimble like a sports car, yet with plenty of leg room and a humongous trunk, the S8 gets my vote for the best high-end sports sedan of all time.
Fast, handsome, unobtrusive, the S8 gets my vote for any long-distance car trip. Seats and legroom are excellent. Acceleration from 65 to 85 (or from 85 to 105 -- but I wouldn't know) is tremendous. The price you pay is poor gas mileage. We love the interior layout and materials. Light on its feet for a large car. Grippy tires, stiff suspension. Excellent sound system. Huge trunk.
This is BY FAR the best Audi I have ever driven, and I've driven quite a few. The ride, power, luxury ... just awesome. Any doubt that anyone has about this car is purely groundless. Quattro = best 4-wheel drive system ever. Cannot be beat. One and only flaw: Doesn't exactly sip gas... but not really hard on it either (a 1998 A6 is harder on gas) since it is made of aluminum. Which is also nice, since it improves stiffness and safety without increasing weight (but increasing price :). Still definately worth it. 360 hp = awesome power. Every possible luxury appointment has been added. Just an all-around awesome car.