The SACD version is absolutely stunning and well worth the cost over the redbook version (IMO). I can not comment on the vinyl version.
I have to say go for the SACD. I haven't heard these two titles but I bought the 45 Modern Cool by Mofi and it is really awful. I'm not the most picky on sound quality of music I like to play but this one turned me off of any Patricia Barber LPs. I couldn't even sell you Modern Cool in good conscience.
Well I have the 45's of Modern Cool, Companion and Nightclub. Keeping the musical selections of each album out of the equation I would rate them sonically
1. Nightclub ( by quite a margin IMHO)
3. Modern Cool
I agree with sonofjim that Modern Cool is disappointing but add that the 33 1/3 offering of "A fortnight in France" is well worth getting - excellent in every way!
As you may have guessed I am a Patricia Barber fan.
I have the 45 set of NightClub, and high res files burned to a (pun intended) Gold MO-FI blank cd using Exact Audio Copy. The lp version has more atmosphere. The CD has more dynamics. Both are stunning.
Either format (SACD or 45 LP) will make you happy for NightClub. Pretty much a can't lose proposition.