Right here. Listen to the lyrics in the Whos music(all of which they wrote themselves) it blows Zeps away. The Who always had a message Zep had none. Keith Moon was a better drummer, Entwistle a far better bass player and Daltry arguably had the best voice in Rock and Roll. The only place their better is on lead guitar but Towsend plays better rythm guitar and his power chords cant be beat. The Who are a far mor intellectual band than Zep with a much more variety a greater writting talent. Ill take Whos Next over any Zepplin album. Zepplin arived at the end of an era and cashed in on all that had done before them.
Zep intentionally made sure their music didnt have any socio-political messages. It was meant to deal with the basic feelings and emotions in life, not be a political diatribe. If you want intellectual, read an essay. Long after people start asking "Whats that supposed to mean?" about Who songs, Zep songs will still have meaning as they are not tied to a specific political era.

Also, I would put Bonham and JPJ against their counterparts in The Who anyday. Voice is pretty subjective.