I'd venture to say that the SLS system is better for sheer comfort (diplomat-in-the-back-seat ride), although handling on the twisties is sacrificed somewhat compared to the standard springs/shocks found on the 420. The SEL cars are also less agile than the SE cars, but they were really meant for the diplomats anyway. I really love being able to put four adults and all luggage into the trunk and have the car sit just as nicely as when I'm in it alone. It's not often I do this, but when I do, I smile when my passengers compliment the ride.