Larry (Cello), are you interested in any particular genre of music when you ask about the Speakers Corner reissues?
For classical, the Decca reissues are a little hit or miss. They are of overall of good quality, but a lot of them are not "outstanding." The Mercuries are pretty uniformly outstanding.
Of the Decca reissues, I agree with ThomasHeisig's recommendations, and I alos very much like:
Albeniz, Suite Espanola, SXL 6355
*Britten, Peter Grimes: Four Sea Interludes, SXL 2189
Debussy, Images pour orchestra, CS 6013
Falla, Three Cornered Hat, SXL 2296
Herold - Lanchberry, La Fille Mal Gardee, SXL 2313-45 (45rpm issue, not the 33rpm)
*Kodaly, Hary Janos Suite / Galanta Dances, SXL 6136
*Mendelssohn, Hebrides Overture (Fingal's Cave), SXL 2246-45 (45rpm version - whether one will like this is system dependent, many reviewers didn't like it, but on a well set up system, it is superb and demonstration quality)
Prokofiev, Peter and the Wolf, SXL 2218
Rimsky-Korsakov, The Tale of the Tsar Saltan Suite, SXL 2221
*Rossini, Overtures: various, SXL 2266
*Shostakovich/Borodin, String Quartets, SXL 6036
The Mercury reissues are all incredibly good. I've particularly liked the following:
*Bach, 6 Solo Cello Suites/Starker, SR3-9016
*Brahms, Sonatas for Cello and Piano/Starker, SR 90392
Marcel Dupre Organ Recital, SR 90169
Mussorgsky, Pictures at an Exhibition: -pf version/Byron Janis, SR 90217
Prokofiev, Romeo & Juliet: Suites 1 & 2, SR 90315
Respighi, Ancient Airs & Dances, SR 90199
*Schoenberg, Five Pieces for Orchestra, SR 90316
*Schuller, Seven Studies on Themes of Paul Klee, SR 90282
I haven't heard the Copland/Appalachian Spring LP, but reports from others indicate this is very well done, too.
I've asterisked (*) the ones that I think are sonically outstanding and not to be missed. All of the ones I've listed I'd recommend if the music appeals.
In other genre, the Verve "Ella and Louis" is excellent, and they did a very good job with the Impulse "John Coltrane and Johnny Hartman" reissue. And, they did a very nice job remastering the varous Ella Fitzgerald "Songbook" recordings. I've also enjoyed my copy of "Gerry Mulligan Meets Ben Webster."
If I were only going to pick 5 classical titles, I'd focus on the ones I asterisked.
Hope this helps,