i would say it depends on the type, age and price of the car being sold as to the best place to try. when i was selling my impreza i tried free adds and gumtree first and had nothing but time wasters for 2 weeks most of them texts to see if i wanted to swap or px with some wreck. so i up it on autotrader and it sold in a couple of days. it was a clean standard car if it was a tarted up boy racer ca. i would have gone to piston heads first.