I have been selling cards privately for Net 54 members (and non members) for a few years now. I have a private client list, set up at most major east coast shows and the national. On any cards over $10K my commission is a measly 7.5% - considerably better than any auction house and Ebay! For strong cards I can usually get strong prices - best part is if I don't get the price we agree to, it DOESN'T sell to the highest bidder! Contact me for more info.
My vested interest aside, I do not believe auctions are the best way to sell most cards. The cards that make the most sense to me to be auctioned are the high demand low supply examples - (think super high grade major rookie cards), where a truly competitive market can be tapped. For cards that have a good supply and clear market value - sellers are just giving up a much larger % of the proceeds than they need to - usually between 15 and 25%
Regarding the auction house question - I believe there is a group of "better" auction houses. Like DJ - I think some houses are better for certain items. I also believe how a house writes a description, takes quality images and where/how they show the card(s) make a HUGE difference.