I won't discuss the merits of Pablo Casals' version of Bach's Suites for Solo Cello, other reviewers have already done that. I will note that he ranks in the very top tier out of all the 12 versions I own. My other top tier favorites are Navarra, Fournier, Starker and Thedeen.
I do not own Ma's latest version nor Rostropovich's version, but I have heard them both. I find Ma to be too slick for his own good - he is indeed so technically correct that he plays the notes a bit too perfectly and in doing so somehow loses the essence of the music... if that makes any sense? Ultimately I do not find Ma convincing, a computer could be programmed to do the same thing. Rostropovich, however, is just the opposite, too sloppy (or some would say too romantic) - he just doesn't sound like Bach to me. I do like a few of his interpretations, but overall I think he misses the mark more than he finds it. I do not mean to suggest that both Ma and Rostropovich do not have their moments or that others have not found them satisfying, but overall there are other performers that just do a better job for me in terms of what I find important. My favorites are not going to be the same as yours all the time. But, at least now you know where I am coming from and where my biases are.
For Casals, the main issue is the sound quality of the various versions that are available. There is the older EMI version, the Remastered EMI, Naxos, Pearl, Opus Kura and Classica D'oro. Out of these choices, which one has the best trade off between noise reduction and the music? These are all sourced from old 78's recorded in the late 1930's, but each uses a different approach to noise reduction. I started off as most of you probably have by listening to the internet MP3 sound bites of all of the various versions - MP3s are not exactly the best way to make a judgment call on sound quality, but I did find that the two versions on CD that I did eventually purchase actually sound very much like the MP3s - there were no surprises in that regard.
So, from that listening perspective (MP3) I can tell you that I was not impressed by the Naxos version nor the Classica D'oro version. Naxos sounded hollow, boxed in and constricted and the Classica D'oro just sounded very processed. I realize that many reviewers praise the Naxos version, but I found the MP3 sound bite to be very constricted - again, this is only the MP3 sound bite, so take it for what it is worth. The MP3 of Opus Kura had a lot of hiss, the most of all these versions, but it also had a very full sound. The Remastered EMI MP3 also had a full sound, but with only moderate hiss. The Pearl sounded decent as well, but perhaps not quite as good as the Opus Kura or Remastered EMI. The Pearl was done somewhat earlier than all the others. So, I passed on the Naxos and the Classica D'oro for quality reasons. I also passed on the Pearl and instead purchased both the Opus Kura and the Remastered EMI versions, as those were also the ones done most recently and hopefully with the latest technology. The Japanese Opus Kura label also has a very solid reputation of valuing musical integrity over all else.
A quick comment on the two EMI versions. Most critics did not like the older EMI version because of overdone noise reduction. I have not heard that version, nor do I ever want to considering the many negative reviews I have seen! However, EMI remastered these performances in 2003 and this has apparently resulted in a much improved product.
O.K. now on to the comparisons; for hiss levels, both the Opus Kura and the Remastered EMI had quite a bit of hiss and surface noise. The Remastered EMI wins with less overall hiss noise and somewhat lower surface noise as well. The Opus Kura clearly has more hiss. It's not always a whole lot more, but it is more and it is more noticeable on some tracks versus others. But, note that the hiss levels can always be adjusted very easily with a graphic equalizer or more preferably with a noise gate. I did make an experimental CD-R copy of the Opus Kura on a CD-R with a noise gate (using Nero) and the result was very good and comparable to the Remastered EMI version in terms of hiss. Even so, if hiss is your major concern and you don't want to mess with a noise gate then just get the Remastered EMI version.
However, if you ignore hiss as a factor, which version sounds better in the living room? And by the way I have an audiophile quality sound system. Here Opus Kura wins hands down. There is no comparison. Opus Kura has all the room ambiance and lower bass tone, overtones and frequency range that the Remastered EMI version has filtered out. The Remastered EMI has no low bass where all the overtones reside - it's just not there and as a result the mid bass stands out more. I must admit that this approach has it's own appeal as it gives the illusion that the recording is both sharper and tighter sounding than it really is and it does bring out more of the mid bass, but the reality is that you are not getting all of the music as originally recorded. Still, it does not sound "bad" and perhaps this is a good trade off. The Opus Kura, on the other hand, fills the room with all the music, including all the lower bass overtones and makes it seem like Pablo is in the room. If you turn the Opus Kura up loud and go into the next room you would think Casals is actually in there playing live. The Remastered EMI in the same test sounds cleaner, but without the deepest overtones it sounds less like a real cello and more like just a deep toned viola - this is a solo cello we are talking about and you don't just EQ out the tonal quality of the instrument (and the room ambience) without losing some of the realism. That being said, it really comes down to personal choice. After listening for a few minutes the ear adjusts to either version. If you did not have the more natural sounding Opus Kura to compare to you would never know what you are missing with the Remastered EMI version. On the other hand, some listeners will actually appreciate the different tonal emphasis on the mid bass that the Remastered EMI offers. I did an A-B blind test with a friend who noted immediately the lack of bass in the Remastered EMI, yet still enjoyed listening to that one as much as the Opus Kura. She did not have a particular preference for one over the other, but they sound so different from each other that at first she thought these were entirely difference performances from different artists! Obviously, some of you will only care about getting rid of "all the hiss", while others want "all of the music." You know who you are. The Opus Kura version strives to keep all the music regardless while the Remastered EMI compromises a bit to lower the noise levels.
A few comments on listening in the car; I really cannot tolerate much hiss in a small confined environment like the car where it can really drown out the music. So, I made my own CD-R recording of the Opus Kura with the NERO noise gate set at 62db for the level and 30db for reduction. This works very well in cutting the hiss down to size and still retaining the music. The only problem with noise gates is that people tend to overuse it - just a little is enough! I did the same with the Remastered EMI at a slightly higher level (70db) and 30db and this also gave a fine result in terms of acceptable hiss levels. Because the three-dimensionality and room ambiance is not as much of an issue in the car environment, I would say that either version (the Opus Kura or the Remastered EMI) would work fine in the car - and if you happen to also have a graphic equalizer the right adjustments might also help make a difference.
Here's the bottom line. For the best sound in your living room, my personal choice is the Opus Kura with the full range of sound, but with more hiss and more surface noise. The Remastered EMI, however, is a fair enough alternative with lower hiss levels and hardly any surface noise (most of the time) and an emphasis (rightly or wrongly) on the just the mid bass. For the car, I think either version works out o.k., but only if you do some remastering yourself with a noise gate to make your own personalized CD-R version that cuts down the hiss.
I hope this helps.