I would say the black Mickey ears are slightly rarer than the gold, so you could probably get more for them.
As far as a fair hat trade for the gold ears, I'm not entirely sure, but I would say the hats available during last year's hat month (Musketeer, Green Flip Cap, maybe Sorcerer Mickey ears, but a lot of people don't want to trade theirs, and whatever the last hat was. I can't remember offhand.)