I test drove a ML500 about 2 years ago and it was pretty terrible. However I hear the new ML is pretty decent and completely redesigned. I have a BMW X5 and it's a great ride, if I were to buy a replacement for the X5 I would have to go with the new Range Rover Sport. Xapster from teeniesxxx has one and it's pretty incredible!
The Porsche Cayenne is nice but I can't get over how ugly the exterior is but the inside is pretty plush and has some nice features.
Anyways hope this helps
DH