Karen McTavish recommends an assortment of embroidery scissors. The reason being they have wickedly sharp points and the smaller blade size can better allow you to get into the nooks and crannies and small notches trapunto designs often entail.
I just purchased some at this spring's MQX show that have oversize handles but small blade (approximately 3", may be less), and a very sharp point. Sorry, I don't remember the manufacturer but when I stopped at the vendor booth and asked for the best scissors for trapunto that is what they sold me. I haven't had the opportunity to use them yet.