Selling off the RPG books has gone smoothly. There's a fair demand for D&D books of all vintages. Get outside of D&D, and the demand is far softer.
I can sell some comics by putting them up on "buy it now" and waiting. Sometimes I don't sell something at auction, increase its price, and watch it fly out of buy it now. More often, however, books languish.
The stuff that sells the best are the "cool" board games, such as Civilization and Talisman.
All in all, if you can gauge a good price on an object, selling as "buy it now" is the way to go.