I guess that would be either AS Sports or the Contemporary - as they have the official pin trading nights.
Mickey's Pin Trading Nights
Thursday nights at the All Star Sports Resort 7 to 10 p.m.
Friday nights at the Contemporary Resort 7 to 10 p.m.
I have only been to the Contemporary one - loads of traders come & they sometimes release special pins on those nights so you may get lucky.
It is also fun to go and look for pins at the hotel pin carts they sometimes sell out less quickly than the parks - though of course there is less choice. You can also sometimes find cool pins on the lanyards of Cast Members at the Resorts - so it is worth a look.
Hope this helps,
Claire