Wife bought a 2011 ML550 (not the hot rod ML63). Car needed brake pads all around by 22000 miles. Other than that, it was a rock of reliability when we traded it in with 45k miles on it. My biggest complaint with the car was the sterile feel....road feel was just never great making long trips a pain. Also, I always hated the damn cruise control system since all of our other cars had the controls on the steering wheel, Mercedes has to be different with a little lever next to the turn signal stalk. Come to think of it, I didn't like the column mounted shifter...not sure if the ML63 is the same or on the center console.
She replaced it this year with a 2013 Range Rover Sport Supercharged with the Silver Package. Car is epic. Great road feel, the air ride is awesome and the power is very good (510 hp). Pulley and tune puts you at nearly 600 crank hp for around $2400.00. Also, the Rangie does have better visibility than the ML out the sides and more user friendly mirrors (bigger, lol). The interior also is at another level over the ML she had.
The 2014's Range Rovers have been updated and are even lighter so they'll be faster with better handling.
I've boycotted the Jeep/Chrysler line until they start selling vehicles with computers that aren't locked down like a virgins chastity belt.....not to mention there is only about a $12k difference between the Jeep SRT and the 2013 Range Rover Sport Supercharged.
Good luck with you search,
George