Unless youre in a rush, or dont want to mess with Gun Broker, etc, put it up on consignment. Doing so, usually brings highest dollar, as the shop will try and sell it for as much as they can, as they now have an interest in it. They normally take 10-15% of what it sells for.
Ive sold a lot of guns this way, and always made more than the shop would have offered, and in some cases, more than trying to sell it myself.
The shops know what stuff in your area sells for, and what they are likely to get. I used to use one shop, that always had prices on new guns that I considered "high". I rarely bought guns off them, mainly because of that, but they always seemed to do a brisk business. When I put guns in for consignment, if they were in good shaope, they would put them up at just under new prices, and I usually got what that brought, less the 15% they charged.