Some neutral info on LD vs Bluray from a person who has a lot to do with the topic. I have discussed all of the following with both sound engineers and computer scientists. And I have, of course, put in a lot of my own experience.
The first important fact is, that until the early 90s movies were recorded in stereo (or mono before that). Then, in the early 90s, Dolby Surround came up. When it comes to sound engineering this was a significant seizure.
Laserdiscs were developed in the mid to late 70s (depending on how you count). Back then they were called Laservision-Discs and had but a single analogue-stereo-track on them. In the mid-80s they got an additional digital stereo track and were renamed Laserdisc.
Both tracks were compression-free. And as the Laserdisc-system was a rather prestigious enterprise the Laserdisc Audio-Masters were often, though not always, direct copies of the original film masters (or at least of copies of them).
And: While the master-tapes of a film are likely to deteriorate over time, the Laserdiscs data-layer is well protected by approx 2mm of a protective plastic-layer. This is as close as a time capsule for the sound as it gets.
So, when it comes to films of the stereo-era the Laserdiscs of those films have pretty much the best sound that anyone can hear them in at this point in time.
Three things stand in the way of getting a similar quality today. The first one is, as stated, deterioration of the originals. Today those originals would have to be remastered first. Remastering always means to change the original because you have to more or less estimate what data has been lost and then creatively re-add it. That process has to be overseen by an experienced audio-engineer. Those cost money - which most releases of older films aren't allowed to do, except they are classic blockbusters like Star Wars (where the companies have to uphold a certain reputation).
So usually some doofus intern, or a former employee who was fired and then rehired as an intern to save money will hushhush the whole procedure and then upscale it into - the second problem - a 7.1 Surround soundtrack that is then - problem three - mildly compressed because even on a Bluray there's no space for 8 uncompressed audio channels.
So, while the Bluray is, theoratically, capable of containing more data, and thus higher quality Audio than LD, older films are prohibited to have that quality on BR due to the passing of time, money-issues, carelessness, marketing strategy and sheer physics - because: Though the compression of the Bluray is called loss-free there simply is no such thing as a loss-free audio-compression. There is a compression that is so relatively loss-free that you won't hear the difference on your average stereo. But - trust me - on a Studio-Monitor it's like comparing an oil-painting with its course, 3-dimensional surface to a very high-resolving carefully lit photo of that same painting. It may fool you for a certain time but it stays oddly artificial and flat.
Fine colourings get lost first during compression. Espacially voices that can have an almost corporeal presence on Laserdisc loose a lot of their shape and physical weight.
In an action movie that doesn't really matter. But listen to a monologue like Brando's Horror-Speach form Apocalypse Now - and it's worlds apart. On LD you get to feel an actual physical imprint of the actors charisma.
However all that counts for older movies. The picture changes when it comes to films of the surround-era.
Here you simply can't give definitive statements anymore. Laserdisc wasn't made for Surround. It simply had no space on it left for additional tracks. Thus the implentation of it on LD is, by todays (BR-)standard, rather poor. The Dolby data-rate on LD is even smaller than it's DVD-counterpart. The later DTS LDs have about twice the bandwidth of DVD but still a lot less than BR. But LD still had it's uncompressed Streo-tracks.
So for films from the 90s it really depends: Was the Film made with alternate Surround and Stereo Versions (Dolby wasnt very common in theatres then)? Was there a real stereo version on the disc plus some additional effects when you had the equipment or did you miss something when you had no Surround? Etc.
Generally the LDs from the 90s still kick the DVDs butt. But not necessarily the BRs, which was designed for maximum Surround-performance. Unimportant re-releases of not-so-succesful movies will still sound better on LD due to careless mastering on BR (many BRs even contain a DVD soundtrack that has merely been decompressed and then put on the BR, unaltered).
Also it's a matter of taste. LDs usually sound more "mature", balanced, lucid, while BR cleary puts an emphasis on spectacular effects like lighnings, explosions or objects audibly moving from one side of the room to the next.
Personally, when watching a BR I sometimes feel treatd like a child that has to be entertained constantly with new, exciting sensations every couple of minutes.
Which makes sense for some movies, like Independence Day, where I absolutely prefer the BR . - But I'm definitely NEVER gonna buy a Dolby-True-HD-7.1-Master-Version of Breakfast at Tiffanys...