Cast iron is the most heavy duty and probably the best tub material available for the long term. Acrylic is a decent tub as long as it is installed properly (with a mortarbed) but the surface is still not as rugged as cast iron. Americast (not made of cast iron) had problems a couple years ago and I don't know if they got solved. I heard it was a problem with the coating not wearing well at all.
If you have never made a mistake, you haven't done much.