'My choices are Zillions of Stamps, APS Stampstore, StampWants or
ebay.'
I've never heard of the first three of these but will definitely give them a go in future.
So far, I've just been buying on
ebay, Stamps2Go and Delcampe.
But having had two items not arrive recently - one an item that I won on
ebay, the other that I won on Delcampe - I'm feeling rather burned and won't be doing much buying for a while.
In terms of selling,
ebay seems the only place to be. I have sold a few things on Delcampe for satisfactory prices but it took ages for them to go.
By contrast, you can get a lot of attention on
ebay very quickly. No matter what you're selling there seems to be someone out there who'll be interested in it, even if they don't always end up bidding in the end.
For example, I sold a North Korean stamp recently on
ebay - getting the bid the very first day it was listed - while two sellers have the same stamp sitting unsold on Delcampe for (I think) rather less than I was able to get for mine on
ebay. The fellow obviously wanted the stamp a lot to bid for it immediately, but must not have been aware of Delcampe.
Overall, I think
ebay is the best place to sell stamps; the problem I have is rather with Paypal and its pernicious policy of punishing the seller if an item fails to reach the buyer (or the buyer
says that it hasn't reached him/her).
Unfortunately,
ebay obliges seller to accept Paypal.