EM's = 5 ball
Very early SS (essentially EM games with electronics) like Playboy, 6MDM, Hot Tip, Cleopatra = 5 ball / 3 ball for widebodies
1980 and all newer SS starting around Firepower, Black Knight = 3 ball
This is how I remember all the arcades I regularly visited in the late 70's / early 80s. And as CactusJack said, prices were raised to 50c soon after.