Scierra C'thru(same as Prologic XLNT Spectrum) for a fluorocarbon. Currently use it in 25lb, for the boom section of my hinged stiff rig and it knots very well.
For my stiff rig I use 20lb black amnesia as a boom and a flurocarbon hooklink. I use the stiff rig Terry Hearn used in his Tel and Jacko estate lake video.