1975 is my favorite tour...aided in no small degree by the amount of many excellent soundboards (sounding better than soundboards from other tours). I tend to listen to the '75 shows on their anniversary dates when I can. It can be a bit much at times...yes, there can be too much live Zeppelin at some point. And, this year...it wasn't quite as enjoyable as it has been. Maybe I've overdosed on these shows in recent years.
In 2011, I did some spreadsheet calculations using my iTunes star ratings for each song of each 1975 show to calculate which show would come out on top. I even did a variation with weighting some songs (OTHAFA, Kashmir, NQ, D&C). That was a few soundboards ago and since I'm sitting at home with time on my hands...I decided to do it again so I can comment with some competence.
For the record, the only '75 audience shows I have are the LA Forum tapes. I'm usually pretty ambivalent about non-soundboard recordings, so my '75 collection isn't as extensive as others'.
CAUTION: Geek zone ahead.
Unweighted, my top five in order are: 2-12, 3-11, 3-5, 2-14, 3-27. If counting Earl's Court, 5-25 would be 3rd
Weighted switches it up a bit: 3-11, 2-12, 3-5, 3-27, and a tie of 3-3 and 2-28. 2-14 falls to 6th (tied with 3-19) and 5-25 would be 7th.
The "average" score for a US show was 4.01 (out of 5) weighted and 5.38 weighted. Both 2-13 and 2-16 were 4.00, so I guess they're average shows. And, 2-16 and 3-4 were right on 5.38 for weighted.
I'm surprised 2-12 stands out here. It IS a very notable show and for recording quality at least it should be in every collection. But...I thought some of the recent '75 SBs had surpassed it in overall show quality. Maybe not. Or...maybe subconsciously I'm using 2-12 as a bar for every other show.
I view 3-21 as simply another very good 1975 soundboard rather than a Holy Grail (Deus Ex Machina). I was surprised to find that based on an average of the average, 3-21 comes out "below average" weighted (5.00) and unweighted (3.93). Haven't listened to it for more than a year, so maybe I'm due.
Other below average shows:
2-10 (surprised, but I don't have any 5-star tracks here)
3-10 (always saw it as a dud...but a 5-star NQ)
3-17 (this one also a dud, at least early...no 5-star track)
3-20 (very surprised by this, but hurt by an average D&C and only NQ gets 5 stars)
The first two LA shows, but this is probably me grading the quality of the audience recording rather than the performance
So, that's what I get using my head. A mixed bag....
Using my heart, some years ago I landed on 5-25 as my ultimate LZ live show just because the vibe is so amazing. Even though I'd put it top, I don't think any one song that night is a "best ever," so it's a bit ironic. And...I've never bothered with the audience recordings from Earl's Court. Maybe I should stop hoping for SBs from those. As for U.S. shows in '75, my favorites show up well this way (3-11, 2-12, 3-5, 3-27)
By the way, I don't have a single performance of NQ ranked less than 4 stars. Always a highlight of a '75 show for me (all-time fave is 5-24).