A Fistful of Dollars (1964)

1984 CBS/Fox Hi-Fi VHS: Heavily noise gated, unlike the CBS/Fox LaserDisc. The loudest passages (those that are least gated) still sound worse than they do on the LaserDisc. Interestingly, some scenes run fractionally longer and others shorter compared to the LD, so it's not just the same base transfer with further manipulation.

1985 CBS/Fox LaserDisc [4556-80]: By far the least manipulated and best sounding version of the film's original English mono mix. Plenty of hiss and distortion especially during any music, but the later releases rectify this through aggressive noise reduction and sound muffled. About 2.5 minutes of footage are missing.

Edit: About 20 seconds at the end of the film (1:38:50, UHD timecode) use Italian dialogue - the undertaker's faint line ("Let me see... Five seven") is in Italian, and a few of his unintelligible grunts here are different than they are in the later LD and the '99 DVD. I suspect everything after 1:38:50 is lifted from the Italian soundtrack, but most of this is obviously the same music present in the English version.

1988 MGM Hi-Fi VHS: Like the 1990 MGM LaserDisc but with moderately less hiss reduction. Still quite muffled compared to the CBS/Fox LaserDisc.

1990 MGM LaserDisc [ML101796]: Heavy noise reduction compared to the CBS/Fox LaserDisc. The first 59 minutes sound mediocre, but the rest of the film (except the final couple minutes) sounds downright awful - possibly sourced from inferior elements, or (for whatever reason) subjected to obscene amounts of NR.

1999 R1 MGM DVD: The first 59 minutes sound like the 1990 MGM LD, but the rest sounds better and more in line with the first hour.

2005 R1 MGM DVD (Special Edition): A downmix of the 5.1 with comparable levels of noise reduction to the 1999 DVD.

2008 Ripley's Home Video Blu-ray: The opening music (3 minutes) is spliced in from a modern remix that uses the wrong cue and is pitched lower than the opening music in the theatrical mix. The closing music (50 seconds) is also a remix of the wrong cue. The bulk of the film seems to be the theatrical mono mix and sounds a bit clearer than the 1999 MGM DVD, but not by much. There are many clicks throughout the film that aren't in the CBS/Fox track.

2011 MGM Blu-ray: Identical to the SE DVD.

2013 Universum Blu-ray: A downmix like the SE DVD but with additional dynamic range compression and non-specific filtering.

2018 Kino Lorber Blu-ray:

Film Foundation: "The music was remastered using original 35mm and 16mm magnetic soundtracks deposited at Deluxe in Los Angeles by MGM. The final mix included the remastered music, the 35mm and 16mm music and effects magnetic soundtracks, and two English-language optical track negatives. Opening and closing titles were restored from a combined first-generation interpositive."

A very obvious remix with dialogue that's moderately NRed but generally more natural than the dialogue in any post-CBS/Fox release. The effects all seem correct, but I haven't confirmed this in detail. The music cues appear correct too, but their increased fidelity relative to the dialogue is incredibly jarring. I easily prefer the CBS/Fox track, where the music doesn't feel like it's playing from a CD as I'm trying to watch the film. The 5.1 on the disc is marginally more muffled, but it's also a new mix that mainly seems to spread the music into the surround channels.

Edit: On closer inspection, there are a few content-related differences. Using UHD timecodes:

• 14:48: After Eastwood says "I don't think it's nice, you laughin'", the other men immediately stop laughing in the original mono mix. In the new remix, they continue laughing for two seconds.  
• 40:29: A final "ya!" is missing in the remix.
• 41:58: The line "Who is there? Come out!" is missing in the remix.
• 1:06:41, 1:06:49: During the chase sequence, two loud instrumental (ocarina?) whistles are missing from the score in the remix.
• 1:24:55: Eastwood's first gun cocking sound is missing in the remix.
• 1:38:37: After Silvanito  says "Adios" at the end of the film, the score in the original mono mix slowly gets louder over about 30 seconds, but in the remix it starts loud and stays loud.
• 1:38:50: The undertaker's final (very faint) words are missing in the remix.
  

It's worth noting that the score in the remix is ~always significantly louder relative to its dialogue and effects.

2022 Kino Lorber UHD Blu-ray: The same remixes included on Kino Lorber's 2018 blu-ray.

5/26/2022: Added the Kino Lorber UHD, more details to the CBS/Fox LD and 2018 Kino Lorber blu-ray summaries, and a comparison clip.
6/14/2022: Added the 1984 CBS/Fox and 1988 MGM Hi-Fi VHS tapes