If I had to pick Vegas shows, I probably would go for those shows that are a little unusual, like a change in the lineup and such. It's been a long time since I reviewed by audience recoding collection, and over the years I have forgotten some exact dates, but off the top of my head I'd say:
8/18/75 OS - I like this entire abbreviated season, both for the song selection and the effort Elvis puts in. This show has a good song selection and it even has a snippet of "Your Love's Been a Long Time Coming" (piano intro only).
9/1/74 DS and MS - These two shows put the CS of 9/2 in better perspective - Elvis was clearly angry on 9/2, but not only on 9/2 - you can get some context for his remarks from these shows.
12/3/76 - Contains a great version of "What Now My Love" - when I first heard it I didn't know what show it was from, so I was shocked to learn it was 76 - great stuff!
12/15/75 - This entire season is superb in my opinion, but I really enjoy this show - some powerful performances, including It's Now or Never.
8/7/72 MS - the first live performance of Steamroller Blues, and Elvis gives it an unusually funky treatment
8/6/73 OS - an unusual opening - a funky 2001, followed by Trouble and Raised on Rock, plus Memphis Tennesse later in the show - pretty cool. Wish there was a good quality release of this.
12/12/76 - the final Vegas show - historic for obvious reasons, but Elvis is in good form and the show is longer than usual.
12/10/75 - a really unusual show, with Can't Help Falling in Love performed second...a sincere version, followed by When My Blue Moon Turns To Gold Again and (if I recall correctly) a snippet of You Don't Know me...overall a nice, committed show with Elvis enjoying himself.
Those are ones I can think of off the top of my head...I know there are more, but I'll have to relisten to remember!