I agree with BBF, this is really apples and oranges; Metal verses Rock, 2 bands very divergent in their style, lyrically and musically.
Musically, the Zep is a vastly more talented band, Page, Bonham, and Jones did more with 3 pieces than the Who ever could, and they relied on one lead vocalist, unlike the Who, who had the luxury of 2, and my preference was always Pete Townshend over Roger Daltry, in fact I prefer Pete Townshend’s solo career over the Who as a band.
If Led Zeppelin had a weakness, it was their penchant for doing covers, not that that is a bad thing, but Daltry and Townshend were better songwriters, some of their stuff was just flat brilliant, even if the band lacked the Zep’s musical talent. That was the same knock for years on Pink Floyd, average musical talent, unbelievable songwriters, it wasn’t until Sid Barrett went totally nuts and they replaced him with David Gilmour, an extremely talented guitarist, that they started to be recognized as a musically talented band to complement their ensemble songwriting (mostly Gilmour and Waters) which IMHO is absolutely the best the world has ever seen outside of Lennon and McCartney.