Definitely based on who you booked with.
but in '07 we were allowed to trade our pin with the CM. Not sure if you still can. DS and I chose to keep our Costco Travel pins (not that they are Costco Travel themed, but they were the ones that came with the package), and DH chose to trade his.
By the next day we ALL had bought new lanyards as our included lanyards were huge and scratchy.