I have driven both these cars, my company is a vehicle export company out of Japan, I attend auctions and usually am buying small family cars and SUV's for car dealers around the world...But every month or 2 I get the magical special order in for one of these high end babies, which means I have a week to deregister it and stuff...put another way, I get to play with them for a week. This is what I have to say about these 2 exceptional rides. The M6 is an amazing drive, pure cruising power, very comfy and well appointed. handles well enough, though a little bit boring for my tastes...but then you look down at the wheel and see the magic little button with "M" on it, click that badboy and it turns this purring cat into a freaking lion that has been starved for sex and just spotted a pack of unsuspecting lionesses! In "M" mode this car is raw and loose and...just plain sick! The RS6 is no where near as nice a cockpit in my book, looks more like a family car and quite frankly I wasn't as enthused about driving it... But that car hammers speed and mixes it up with sick responsive handling that the BMW cant match! To the question...The M6 is my choice...I am a diehard BMW fan, and it suits my kind of driving, very sporty and loose... But the RS6 is no slouch people, I am just Biased as hell The M6 on Top gear The RS6 Top Gear