For a single original cast Cd the 1993 Toronto cast (this company moved to Broadway in 1994) is the best.
If you want the original 1927 text and orchestrations EMI's operatic recording (Complete on 3 CDs) is well worth having though you may find you don't listen to it a lot because of the length. (It runs 3 hours and 40 minutes!)
To recap SHOW BOAT on records....
There was no OCR made of SHOW BOAT in 1927. American labels weren't doing them then.
The first SHOW BOAT cast album was the 1928 London cast. It's really just the key songs but it does preserve Paul Robeson's "Ol Man River." These antique 78 RPM records have been re-released on a budget CD from Prism (PLATCD 733) along with the 1946 Broadway revival cast.
The 1932 Broadway revival got an early cast album on Brunswick that was available on Sony Special Products (A 55) It's not actually all original cast. Paul Robeson and Helen Morgan sing their songs (Ol Man River, Bill, Can't Help Lovin'Dat Man) but the three romantic duets were done by studio singers Frank Munn, Countess Albani and James Melton. This album has just these 6 songs, along with a 2-part orchestral medley. None of the arrangements used on the records match what was heard in the show. So this set is for historical interest only.
SONY reissued the 1946 Broadway cast album on CD a few years ago (SK 53330) and this selection is also paired with the 1928 London cast on Prism. Recorded on 78 RPMS, the sound is a little brittle and the limited playing time cuts the album down to 9 songs (including Nobody Else But Me which was added to the revival) and the new overture created for the revival.
RCA Victor has the 1966 Lincoln Center Revival cast with Barbara Cook heading the cast (RCA 09026 61182-2). It's not a very theatrical album and doesn't get a great deal more of the score than the 1946 set. If you like Cook you are better off getting the Columbia studio cast album she did in 1962 with John Raitt (SONY SMK 61877.)
Although it has been out of print for 15 years now, Stanyan's CD of the 1971 London revival (Stanyan STZ 107-2) is worth seeking for Cleo Laine's Julie. She "scats" a section of Can't Help Lovin' Dat Man, and sings a tender touching Nobody Else But Me. The Cd is a bit of a mess...songs in a strange order that clearly did not reflect the order they were done on stage. (EMI recorded this as a cast album of the revival and issued it in the U.K. as a singe Lp. They also recorded additional material that Stanyan added for the U.S. release.)
The Hal Prince revival opened in Toronto in October 1993 (I was at the premiere and it was a memorable evening!) The Toronto cast Cd was made by Livent and distributed by Quality Records Toronto (RSPD 257) and with a slightly different cover in the U.S. on Livent music (62588-80005-2). When Livent collapsed the rights to this recording went with them, which is why it is not currently for sale. Of all the single CD's cast albums, this one is the best. The shifting of the song Why Do I Love You put off some people. Originally a 2nd Act duet for the lovers, it was given here to Parthy to sing as a lullaby to her infant granddaughter, Kim. Later the song serves as the basis for grown up Kim's Charleston routine. Purists may balk, but I found the change added more depth to the show. And since the revival restored I Have the Room Above Her (from the 1936 film) as another 1st act duet for Ravanal and Magnolia, they really didn't need a 3rd number in the 2nd Act. The whole cast here is exceptional. If you want this CD and can't find it contact me at the e-mail below. Copies turn up used here fairly regularly as the disc got wider distribution in Canada.
That's pretty much it for the cast albums. There are many studio casts.
EMI/Angel did a 3-cd set of the entire score in 1988 including out-takes and supplemental material (EMI A23 49108-2). This features a cast of opera and Broadway singers and is packaged like an opera with a thick libretto containing detailed notes. The best thing about this album is the chance to hear the original orchestrations. I find some of the acting a bit stiff but the singing is glorious. A single CD of highlights presents the score as heard on opening night on Broadway in 1927.
Rhino has a CD of the score from M-G-M's overblown 1951 film. It's not really useful as a SHOW BOAT recording unless you are a fan of the film. The 1936 film is as close to the original cast as you'll ever get.
Cast albums are NOT "soundtracks."
Live theatre does not use a "soundtrack." If it did, it wouldn't be live theatre!
I host a weekly one-hour radio program featuring cast album selections as well as songs by cabaret, jazz and theatre artists. The program, FRONT ROW CENTRE is heard Sundays 9 to 10 am and also Saturdays from 8 to 9 am (eastern times) on www.proudfm.com