Led Zepplin III, with Houses of the Holy a distant second.
Although it is probably passé to say so, the 4th album is their best. It culminated their early blues- and folk-based music, and served as the basis for all their subsequent work. That being said, I love Zeppelin III and Houses of the Holy to the point that it’s hard to dispute your opinion.
Presence.
It’s Zeppelin at their peak creativity and maturity, yet before drugs fully eroded their gifts. It’s also not rife with plagiarism.
Achilles Last Stand is a masterpiece.
Led Zeppelin III, home of the Viking Kitties song.
Definatly 111
Tangerine
Zeppelin II followed by IV and Physical Graffiti
The bass work in Lemon Song is incredible
Led Zeppelin III
“While we’re on the subject - favorite Led Zepplin album”
Any of them at any time. Put ‘em on auto play, can’t go wrong.
Wanna watch something neat? The complete rehearsal show for the 2007 O2 London Reunion. Full rehearsal
https://www.youtube.com/watch?v=UbiuCoXD8L8&t=422s