Of course it is hard for me to compare because the only Ferrari I've ever driven is a 25 year old 308. We've got a Mercedes E-300 Turbo Diesel and I love it. 6 passenger, 38 mpg, the thing rides, handles and brakes awesome. The Ferrari, of course, handles and brakes awesome also, but it's like driving around in a go-cart or a race car (except at 5 mph - in a parking lot the thing handles like a truck.) If you are into performance driving and want the feel and the sound of something made for high speed driving then the Ferrari wins hands down for driving pleasure. If you want the smoothness of a performance luxury sedan, then it's the Mercedes.
If we are "going somewhere", we take the Mercedes. If we're just "going", we take the Ferrari.
I would like the opportunity to compare similar models of both makes at sometime. But for now I'd just say that I like them both, but for different reasons.