Good friend of mine recently picked up an '06 CL600, he went with it over an AMG as it is 'for his wife'
In any event, he tells me it is more than sufficient to get him into plenty trouble. Granted this is about the coupe, same driveline.
I am one that enjoys excess, so I would end up in the S65. Also, I would choose the S600 over the S63. Torque is king on the streets...unless you mean a new twin turbo S63.
Depends what years you are eying.