You cannot say one is better than the other, ACDC are pure Rock n Roll whereas Zeppelin are a mixture of Rock, blues rock, pop rock ect. And as said above it depends on your tatse, they are different, I mean Zepp's my favourite band but I don't go around saying PF are worse then Zepp becuase they are different, and so are our tastes, just because you like a band so much doesn't mean to say others aren't as good.
I better stop before I go round in circles