If you're going to get a C6, make sure to invest in the Z51 package. It makes all the difference in the world. I owned a 1997 C5, and the difference between the two is like night and day. I'm not thrilled with the navigation system only because I would have rather had the in-dash 6-CD changer as opposed to the single CD player.
A very tight 6-speed gearbox that lives up to expectations.