I've advertised mine on the forum, Ebay, Autotrader and Pistonheads. Initially not bothered with Autotrader as they are not cheap!!!, but after 2 weeks of no response, decided to pay and advertise on Autotrader as that's where I (and many more) usually start my search for car hence make sense for me to advertise there. As above, Ebay will have lots of time waster and low ball offers.
Facebook marketplace is good too if you're on it. It free but similar to EBay's time waster and low ball offers.