I just bought the all new 2012 ML350 for the wife and I am really impressed, much, much better drive than her last generation 2010 ML. I was also considering a Cayenne, but for the same price of a very basic V6, I got all the toys in the ML.
The ride is great, power is the same in both, the new interior design, fit and finish is awesome and the looks with the optional AMG sport package and 20"s is just perfect.
I have a Cayenne S, and I dont miss it a bit when I am driving arround in my wife's new ML.

 

I have a 2011 X5 with the turbo diesel v6 and sport package (20" wheels). It is awesome! Worth the $70k price tag.

-SZ

 

Have owned all BMWs all my life. Had the X5 50i and the Cayenne V6 at the same time in the garage. Sold the X5 after two months of ownership. It's true that a fully loaded 50i is about the same price as a well-equipped Cayenne, but it all comes down to one's personal preference in cars - as I was looking for an ultimate driving SUV not just a straight line SUV. BMW and Mercedes often offer the best deals compared to other marques (e.g., Audi and Porsche), since their deals are usually the sweetest between October and December. I got my 50i for almost 10000 dollars off (including all applicable coupons) with all the bells and whistles as well as a whopping near three-ton curb weight. If you are going to own the SUV for the long term, try the Cayenne. If you are leasing, ML and X5 are no brainier; with the amazing incentives and money factor and multiple security deposits, it'll save you a bunch. All in all, you can't go wrong with any of these three choices, just be sure you do not have any buyer's remorse like I did with the X5.

 

Look for a low mileage preowned cayenne

 

Cayenne is much more refine than the X5.
The higher cost is worth it!