If you were picking something to keep for a long time I would pick something with a certain 'timeless' quality to it.
As much as I love my M3, I don't know if the appeal for it 15 years from now would be the same as that of, for example an Aston Martin Vanquish S.
Or even a DB9
These are cars that in my opinion, will be beautiful for all of time.
I was also thinking a CLK63 Black-Series (but I don't think it comes in a 2+2?) Anybody want to confirm that?
Cheers