I love CANDIDE, flawed as it is, and there's nothing I love more than a work that has been heavily rewritten over time. As others have suggested, the original cast album is a wonderful entry point - the original cast is largely definitive and the album zips along beautifully. It’s a great listen and I’d guess is largely responsible for the work’s longevity. I love the LuPone/Chenoweth concert version as well, Chenoweth is at her bubbliest and in great vocal health, and the production, by Lonny Price, leans into slapstick in a very fun way. the 1974 cast album is also a fun listen, and includes full dialogue, but the Prince/Wheeler version of the show is a very particular “take” on the material, focusing largely on the wackiness and the cynicism over the heart or philosophy (the Chenoweth concert uses a version of this script, but makes some smart incorporations from other versions).
Bernstein’s own 1988 recording (which was also filmed for television and available on dvd) is sung and conducted grandly, though it can’t match the original cast for tone or energy. Regardless of Lenny’s propensity to slow things down and, frankly, his tendency to get up his own rear end, there’s a benefit to hearing his final statement on the score and the concert includes a few wonderful songs that aren’t part of any previous version of the score, in particular Candide’s heartbreaking final aria “Nothing more than this” and the silly yet magisterial "King's Barcarolle." It’s also fun hearing opera legend Christa Ludwig cutting it up as the old lady.
So if you want to dip your toes into this score, I think those three or four recordings can give you a pretty accurate picture of it. If you want to do a deeper dive, however, there are other riches to be found. Read on if you wanna get nerdy.
There are, essentially, four scripts of the show in existence, and we’re lucky enough that through pirate recordings, radio broadcasts and a little hunting, we have videos or full recordings of three of them. To break them down, they are:
Lillian Hellman’s original libretto, which is a fascinating tonal mismatch to the score. In addition to the original cast album, there is bootleg recording of a fascinating 1968 concert version in existence, featuring Madeline Kahn and Alan Alda. I have that if you want to pm me, but wasn't able to find a copy on youtube. I DID find this bootleg recording from a 1971 touring production featuring Mary Costa (best known as the voice of Disney's sleeping beauty) which was broadway-aimed but never got there. https://parterre.com/2024/05/23/a-mouth-so-fair-it-must-be-kissed/
Hugh Wheeler’s wacky one-act script for Hal Prince’s immersive off-Broadway production, which I think was a major inspiration for “Natasha Pierre and the Great Comet”. This script got expanded into two acts, with some of the rough edges sanded off, for Prince’s elegant New York City opera production, which was revived on Broadway in 1998 with Jim Dale and Jason Danieley. This is the version we have the most recordings of - both the 1974 and 1998 broadway productions got a cast album, as did the original cast of the NYCO production in 1982. The NYCO production was also filmed for television in 1986, and as mentioned this is the main basis for the Chenoweth concert version, so it's stacked. The 1986 video is on youtube here: https://www.youtube.com/watch?v=VXF_1KJNHs8
John Wells and John Mauceri's edition, put together under Bernstein's supervision for Scottish Opera in 1988, later the basis for Bernstein's 1989 recording. This is the "grand opera" version, prioritizing the score over the story and sticking closer to the novel. Video versions of the Scottish opera production (https://www.youtube.com/watch?v=uQEQNuY6waw) and the Bernstein concert (https://www.youtube.com/watch?v=cMIzHnyuiNY) are on youtube. There is also a DVD of this version by the Teatro Argentina Opera in Rome, but It's largely unsuccesful
John Caird's adaptation for the highly lauded 1999 Production at the Royal National theatre, which leans heavily on the novel and trys to find a compromise point between Wheeler and Mauceri. It largely succeeds, but having sat through a couple of community-level productions of this one it can be VERY long in the wrong hands. No video of this one, but the Cast album is on spotify last I checked and worth a listen!
About a decade ago, Mary Zimmerman produced an excellent adaptation of the material for the Goodman Theatre in Chicago, which went on to play DC and I think one other regional theatre. It was excellent, and the best attempt I've seen at marrying the tone of the score to that of the novel. There's a video of it floating around the internet somewhere, though I don't currently have access. Happy hunting.
Also, check out https://www.sondheimguide.com/Candide/contents.html - an invaluable aid for Sondheim nerds in the early days of the internet, Michael Hutchens compiled a reference for every production of the show in existence, including a priceless copies of the Hellman and Wheeler librettos in full. It was last updated a decade ago, but such a great resource.