I've have both brands but not these models.
Here's why......
I love cars like Mercedes and Cadillac, there nothing but a perfection!
But understand getting such cars will will require extreme care, specially for the cadillac. The Cadillac will run good for about 60,000 then start giving you trouble. The Mercedes will give you at least 80,000.
Despite the 8 cylinder engines, the cars are equipped with heavy duty computerized system!!! which means one small issue, no matter how small it could be; will cost you a lot! Now that's an issue with all new cars, even the Venza, which i purchased last month.
But the problem with Cadillac is that once it goes in the stage of breaking down, it will not stop!!!
Chose carefully, but my auggestion is go with the benz. Once you feel the experience, you can't go wrong.