I have a 1998 C230 and a 2002 C240. Both are very nice cars, and feel like they will be solid for twenty years. But I would guess the 2006 C models with their new engines are noticeably better.

You better get a good long factory warranty if your buying a used C320. Some were made in Brazil.

And there are some excellent new japanese cars for the money of a used C-class.

All new C-class in 2007.