lately my favorite is anything off of Physical Graffiti. This album was the only Zep album that I didnt own or hear alot when I was growing up so it seems still kinda fresh to me. yeah, I know all the radio songs by heart but tracks like "Ten Years Gone", "Time Of Dying", "In The Light", and "The Wanton Song" are climbing my list of all time Zep tracks.
This album seems to be their creative apex, at least that's what my ears are telling me.