It's only 20 guns, and it sounds like you have some free time on your hands. Best value will likely be posting them online at an auction site or posting online for private sale - but it does take the most legwork. Consignment with a local shop is easy, but it can take FOREVER, depending on the product you have and the market you're in - it can draw decent prices, which you share with the shop, so your value decreases. Selling to a shop ensures their profit, not yours.
It's only 20 guns, personally, I'd figure up the costs on packaging and shipping, set my prices, list them online (considering auctions vs. sale listings for certain desirable models), and let nature take its course.