When I wanted to sell my Type R last year, I put ads on Autotrader.com and Cars.com. The Autotrader generated about 75% of the responses I got, while Cars.com only 25%. I got about 100 or so replies total over a few months. The car finally sold to a guy in DC who flew all the way down to Texas to get it. I'd had the car 3 years and sold it for $22k after buying it brand new for $24.8k.
I recommend going with the ~$50 ad on both of them. That allows you to put up one picture. The cheaper one is no pictures and the ~$70 was multiple pictures. I simply started a Yahoo gallery and sent the link when folks requested additional pictures. I'd highly recommend both sites. Your ad will run until you sell the car with no additional fees. You just have to renew it each month (for free), and they email you reminders to do that.