My top 3 at the moment-
I think Earls Court 1975 is the best set of shows the band has ever done. My DVD boot of them of an entire show is my favorite Zeppelin gig ever. The performances on the official DVD are perfect, too.
I also love LA 1977, I have a thing for the 1977 tour. It wasn't the best but it was so legendary and dark which paved the way for some excellent shows. Listen to this Eddie is the highlight for me, my only complaint is Jimmy's one flubbed note at the start of Stairway's solo
O2, London 2007- not their technical best but it is "my" version of Led Zeppelin. I wasn't there but I was there in spirit! After years of being a young fan, the build up to the gig was tremendous. The day of the show was great listening to the radio all day at my high school in Michigan. Love the performance and setlist, and think it is an absolute triumph.
Blueberry Hill is excellent, Seattle 1975 (the longer show), How the West Was Won, Pontiac 1977, MSG 1973 (don't get why the band was disappointing in their performance on the movie, I think these shows were great), Hampton Roads Coliseum 1971, and many more!
EDIT- I mistakenly thought the thread was favorite shows. To answer the thread's actual question, I think Earl's Court 1975 was the peak of Zeppelin's bravado