I traded a 2007 Jag XK for the SL. The Jag is beautiful, the SL is not only gorgeous, it is awe-inspiring when driving. It is more responsive, has a better ride, more power, and better seats--and--it has a hard top that looks great when up. I've owned Lexus, Range Rover, NSX, Corvette, and several Jags and several BMWs--the SL 550 is head and shoulders above them all--it is absolutely the most fun of any car I've ever driven--and that includes the new Aston Vantage V8. The SL is nimble,corners flat, is fast, and somehow still maintains a very comfortable ride. I highly recommend it. The only drawbacks are the price and the mediocre gas mileage.
The way the car drives. It is incredible.
Make the Mercedes "command" system user-friendly. I still don't understand it, even after reading the manuals.