Mr. Smith Goes to Washington (1939)

The 1995 LaserDisc sounds great -- much less noise reduction than the DVD and blu-ray. The UHD disc uses the same audio track as the blu-ray.

(I think the DVD track I was sent is an AC3 to AC3 transcode, but whatever. It's a bit less muffled than the blu-ray, but nowhere near as clear as the LD.)

Update (01/01/2021): Added the first disc of the 1985 RCA/Columbia LaserDisc, which should be enough to make judgements on its overall character. It's not really any better than the 1995 LaserDisc -- I hear a lot more distortion and certainly a fair bit of compression (I don't know much about the analogue LaserDisc transfer process, but if it's anything like cutting a vinyl record, adding some analogue compression would make the process easier, especially if there's too much information to fit on a single disc). The opening music sounds much worse on the older LD, but after adjusting for volume the meat of the film sounds similar but with more distortion.