Each trip, we are sure to get a couple pins that commemorate THAT trip. For example, our last trip was over Memorial Day, which also coincided with Flower & Garden Festival. It was also our first stay at FWL.
So, we picked up a Memorial Day 2005, Flower & Garden 2005 and a Fort Wilderness Pin.
We do NOT trade, because we buy the pins for sentimental reasons, not for the "best investment" type of thing. It's just something to remember our trips.
However, if we see ever find a CM with a "Skippy" pin, we'd be all over that. My DF absolutely LOVES Skippy. Apparently, they made a Skippy pin when Alien Encounter was first out. Can't find them anywhere, now. He's still in it, too! (Are you listening Disney? We want Skippy merchandise!)
To answer your question, I'd say find something that appeals to YOU, there are certainly enough choices. So many that I would make a suggestion. Have a # you want to purchase in mind BEFORE you go looking for your pin(s). If you're only going to get 1 or 2, DON'T buy the first ones that strike your fancy. Without a doubt, as soon as you make your purchase, you'll see another one that you HAVE to have. It can get very addictive!