I went through this debate briefly a few years ago. I concluded that finding good condition vinyl on sixties soul and R&B was not likely. So, I bought both the Stax Singles Set Volume 1 and the Atlantic R&B Box. While there is some overlapping between them, I think both are worthwhile.
The Atlantic box is more mainstream, and has many well known hits, and a wider cross section of eras, as it covers 1947-1974. The artists include The Coasters, Booker T. & The MG's, Ruth Brown, Solomon Burke, Ray Charles, Aretha, Ben E. King, and countless others. As an introduction to R&B I can't recommend the Atlantic box more highly.
The Stax box is more focused on one very special era in American music. It is really a 60's box set, and includes such great artists as Carla Thomas, Otis Redding, the Mar-keys, Rufas Thomas, Albert King, William Bell, and dozens of others. Stax was a more regional, Southern label than the better known Motown imprint, and it there is, in general, a very gritty, very sexy, raw feel to much of it. This is what SOUL Music is all about.
Since the initial Stax box was successful, they have released two additional volumes concentrating on the 70's. Critically, the latter two boxes don't garner the universal praise that the first Stax box does, so they might be better left until you see if you really get into the first one, which covers the cream of the Stax crop. There are also now theme boxes in these musical styles from Rhino, but I don't have any experience of these.
Sonically, I find the Stax set more uniform overall than the Atlantic box. Both are in the clear, clean side of digital, both are from 1991, and on neither does the sound really intrude for me. With the possibility of the high quality job Sundazed is doing with releases, I would endorse buying any of their recordings if you prefer vinyl. I don't have all that much soul on record, but I can tell you that Otis Redding Live at Montery is better served by vinyl, on my system anyway, but I still would not trade the boxes for their extraordinary overviews and the inclusion of many artists I doubt if I would have bought whole albums from. With these huge, sprawling box sets, I actually prefer the convenience of CD unless it is music I want to bath in.
Happy hunting.
[This message was edited by bdnyc on TUESDAY 02 April 2002 at 06:17.]