Drive shaft question mild steel or aluminum?

That's the site I was looking at too. They have a 1020 mild steel, a 4130 moly, and a 6061 aluminium. I think they are all available with the 904 spline and 1350 joints. I just didn't know if I needed anything special. I'm all about having an insurance policy so that's why I'm asking. Is one better than another?