Before this gets into a brand loyalty flame war...I'd just like to chime in with a recommendation for the W220 S500. In my experience it rides better and is quieter than the previous W140. (you can hear the engine, but that is a GOOD thing IMO) Handling is an EASY advantage over the W140. Only gripe being some of the interior bits are not quite what I would want in a flagship luxury sedan. They improved all the measurable traits while lowering the price, guess it had to come out somewhere... True, the S600 might have it on the extreme top end or perhaps pure snob appeal, but the S500 has a solid lead in about every other measurable standard(W220 of course). Only gripe is that it could use far more capable tires given its attributes. Still, everyone has the traits that appeal to them most. The different manufacturers each do something a little different to suit the public. Just drive everything and your butt will tell you what is "best" for you.
Just my opinion...Lee