[Mr.ac]

Always go with the Kelly Blue Book value.
That being said selling it private party always gets you the most value.
As to where to sell it for free:
Craigslist, on parked the side of a busy street with a for sale sign.

Then if you want to pay a few bucks to have it national broadcast any car sale websites.

Lastly if you just want to get rid of it quick any car dealership. Or use it as a trade in. But expect them to low ball you like a retard. You can fight them a bit and get a higher price, but it would no where come near the amount you can get if you sell it private party.