Everything considered, the original quality of the recordings probably makes the most difference whether it was done in DSD or redbook PCM. Having said that, everything else being equal, if the original recoding was done in DSD, it should be better than redbook format.
Also if a recording was done in DSD, it's almost likely that there were a lot more thoughts went into the recording so you probably get more quality playback just because of that - that is the recording was done by people who knew what they were doing. So the majority of gain in quality probably has more to do with the nature of the recording than because of the DSD format.
I once used JRiver to convert a redbook format CD to DSD format, but the playback of both was more or less the same and I couldn't tell the difference. So I guess to make any difference, the original recording has to be done in DSD. That is not to say they are the same, but it is meant to point to the importance of the original format.
And there are also those who do not like DSD format because being higher in frequency, the higher frquency of the DSD clock is more susceptible to noise and jitter. But we are getting into technical area that beyond this discussion.
For historical perspective, back during the infancy of digital recording, the reason redbook format was recorded at such low data rate is because had it done in high resolution (like SACD or DSD), the disc would have been so large to store the extra data rate that it was not practical (because the digital storage capacity much lower in those days). Panasonic actually wanted high resolution, but Sony on the redbook side won out because Sony was able to make the compact disc smaller and more portable.
