I know of : GunBroker, Guns America and AuctionArms.

Are there any others that I'm missing?

Which is the Best ?

What Ya Think?

I've bid on items on both GunBroker and Auction Arms, never had problems with either.  GunBroker seems to be more popular, but both sites seem to have decent sellers...

You've pretty much named the main three.  There are only a few sellers of firearms, in particular on AA, and Gunbroker that I have seen that are selling stuff with no reserve and taking their chances that they are going to come out ok.  Otherwise, it seems like most just tack on pretty high reserves that must be pretty close to what their arms are worth and hope for a nice profit.

You don't see a lot of people on these sites selling stuff just to get rid of it.