OK, I like both bands but I'm more in the Zep camp, and I'll tell you why. In spite of their tendency to borrow from the old blues masters, they were still incredibly creative songwriters. When I hear people talking about Deep Purple as great songwriters, this is what comes to mind. It's cued up right where I want it:
That's not to say that they weren't a great band. I think they were. But I don't put them on par with Zeppelin.
Neither band was Dylan, but even when I was sixteen and Smoke On The Water came out I knew those were god awful lyrics.