I think we did this already in one of teh FINA"s RAINBOW thrteads but briefly:
The original 1947 Broadway cast has just been re-released on CD (
http://www.amazon.com/Finians-Rainbow-Original-Broadway-Recording/dp/B002M2Z3QU/ref=sr_1_5?ie=UTF8&s=music&qid=1256771942&sr=8-5)
The advantage is that this IS how the show sounded when originally done. But it was recorded on 78's, so the songs are abridged to around 3 minutes each and this transfer reveals some surface noise from the masters.
The 1960 revival cast (
http://www.amazon.com/Finians-Rainbow-1960-Broadway-Revival/dp/B000002W1I/ref=sr_1_7?ie=UTF8&s=music&qid=1256771942&sr=8-7) is more complete and has better sound. The CD is technically out-of-print but is available as a CR-R from ArkivMusic.
The 1968 film soundtrack (
http://www.amazon.com/Finians-Rainbow-Burton-Lane/dp/B000IAZNBI/ref=sr_1_2?ie=UTF8&s=music&qid=1256771942&sr=8-2) has that boxy Warner soudnstage sound, and teh re-arranged teh songs to give Fred Astaire a chance to sing (and dance) as Finian. The earlier CD release by Rhinio Handmade includes some extra material left off the Lp, but teh 5,000 copies old out very quickly and that version is expensive when found.
A 1962 studio cast on Reprise features Frank Sinatra, Bing Crosby, Dean Marin and others. It's fun as a "pop" collection, but not a proper recording of the show. It's only available in a boxed set with similar albums of GUYS AND DOLLS, KISS ME KATE, and SOUTH PACIFIC. (
http://www.amazon.com/Reprise-Musical-Repertory-Theatre-Finians/dp/B00004XN1K/ref=sr_1_22?ie=UTF8&s=music&qid=1256772688&sr=8-22)
The Irish rep cast with Malcolm Gets is enjoyable bit I miss the full orchestra as heard in the two Broadway recordings, but the Ferrante & Teicher style piano accompaniment is acceptable. Not sure about the sound quality as my copy has a lot of static. (
http://www.amazon.com/Finians-Rainbow-Repertory-Theatre-Recording/dp/B000641A7C/ref=sr_1_9?ie=UTF8&s=music&qid=1256771942&sr=8-9)
For my money the 1960 cast balances good sound quality with great performance sand covers most of the score, so overall it's the best buy.
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