Damn, El-bent beat me to it!
Seriously though, I’d stick with AT. If you don’t sell by the end of the advertised period then they’ll offer you a discount on a similar or better package.
Also try Pistonheads (tis free).
IME AT will give you the more seriously minded buyer, and IME the ‘no canvassers etc’ has actually meant I’ve not had any canvassers.
Do keep an eye on prices though. I sold our Focus on there a fortnight ago and prices went up and down literally 20% over a single month. Was a bit weird, but got a good price in the end.