To get top dollar, you want to sell it yourself.  Depending on the vehicle, you can sell on Craigslist, Autotrader, Cars.com, CarGurus.  If it’s a niche car or enthusiast car (for instance a Corvette or Porsche) you can try selling in the ‘For Sale’ section on those vehicle’s forums.  For the heck of it and to get a reference, you can try CarMax in person and see what they offer (but usually will be less than if you sell it privately).

With dealers or online sites like Vroom, Carvana, even CarMax, the paperwork is taken care of for you and you kind of know whom you are dealing with (most likely will get a check and not be scammed, but again you won’t necessarily get top dollar).  With Vroom and Carvana, I have heard of horror stories of people not getting their checks (getting lost or not mailed out) - just beware if you try them.  Most don’t sell privately and just go through dealer or online site for the convenience (but again at the cost of less money offered).

Put it online for sale (in CL or Facebook market place).

It really depends on what you have and what condition it is. If it is a junker, sometimes you can get a good price from Carmax, Carvana,..., but generally speaking, dealers gives you the least money. 

privately through internet sites like autotrader

The best way to sell a car is for CASH.

Try Carmax if one is near you. They will give you an offer which is good for a week.