I started with craft thread and sewing thread until a visit to a Fly Shop where I bought Uni Thread in 6/0, 8/0.
My tying is still at a rookie level and I would break the craft and Uni threads.
My dad got me some Griffiths Sheer 14/0 and I will not do without it.
Amazing thread 1/2 the thickness as Uni 6/0 and stronger.