First off, I will only buy about one pin per trip. The rest are traded for.
DS5 likes Haunted Mansion and Nightmare before Christmas pins. In Sepotmeber, it was all Buzz Lightyear pns, but they went away when he started finding Jack Skellington pins!
DD6 has no rhyme or reason to her collection. She has baby princesses, cuties, figments, pretty much whatever catches her eyes.
Me, I don't trade for value. I don't really care if a pin is a LE, a CM exclusive or a rack pin, if it I like it. I like the Americana pins, the Mickey Bears, and the bejeweled ones. I don't get too "into" the CM pins, but in Sept I had to have all of the rear-view mirror pins, and it took the entire week to get them all!