I did a little comparison and did a search on cars.com using the exact same criteria that I'm using right now to find a new vehicle and it came back with two results. - One very good one though, I might have to go look at it. - Autotrader usually comes back with 15 or more.
As for listing a vehicle, I'd go with Autotrader. I can't give you site specific numbers but I would think it's safe to assume that it gets more traffic.
[This message has been edited by p_bubel (edited 4/10/2007 12:18p).]