I voted interchangeables since I've got two sets, but I like plain circs too.
I don't think I've used a set of straights more than once since I got my Boye's set. They made my hands sore from trying to hold them up!
My New Blog: Geek Knitter
I believe in a life of Virtuous Sloth, but it sounds so much better in Latin: otium cum dignitate, leisure with dignity.