Most fitters use the dolphin knife. If you don't what do you use? I used to use the Stanley interlock knife. Good knife.
I used to use the Stanley Interlock but got fed up with them seizing up when I used to try and open them. I use a dolphin now. The dolphin seems to be very good at opening the interlock knife
hookys for doing vinyls just prefer the feel/size of the interlock for getting right close to the wall