Lee had not begun making molds when I first started casting, and those Lyman SC's owned by my neighbor's dad were instrumental in determining my own initial purchases. I bought a Lachmiller and a Cramer mold at a Yard sale and for years I used them--still have them, though both have been replaced by 4 or more cavity molds now. Both are iron alloy molds.
I am not a fan of Lee molds for beginners. It is easier to learn on a steel or iron mold than it it is on an Aluminum mold. However, for the more experienced caster, those 6 cavity gang molds are the bomb for producing piles of boolits fast.