30 for most vinyl, 60 for thicker vinyl like reflective, but you must recalibrate the offset when you go from one to the other.
30 degree will do fine on reflective but will wear it out fast. I keep a 30 degree in a seperate blade holder for reflective and only need to adjust how hard it hits and not spend time with the offset.
Years ago, most plotters came with a 30° blade and is used mostly now for thin materials like window tint. In recent years the 45° is the most universally used. 60° blades are indeed for thicker materials and small detail cutting. The 60° is becoming popular as well for reflective, chrome, and metalized vinyls because it stays down in the cut with less downforce.