CD sound quality: original pressings vs regular remaster vs MFSL, etc

In terms of which version of a CD to buy, a general (but not always applicable) rule for playing through good HiFi equipment is that an original CD from the 1980s or early 1990s is preferable to any remaster. The exception is classical music and some jazz where remasters of older recordings are usually better (in classical music and jazz when they remaster they do not add so much compression, as opposed to the ’brick-walling’ often done in contemporary music remasters) .

Most remastering makes things sound better on earbuds and in cars, but not on audiophile equipment. It might sound more impressive on an initial A/B comparison, but your ears will find it fatiguing after a while, and it won’t sound as 'musical'. 

Agree with @duckworp. After hearing some terribly compressed rock CDs on my home system, I set out to find the best quality releases of my favorite rock bands.
I listen mainly to classical and the quality of Redbook sounds so good thru my system, I couldn't listen to the vastly inferior rock albums.

Using the Steve Hoffman Forum and Discogs I researched early releases of Zeppelin, Hendrix, Pink Floyd, Heart (known to be excellent recordings), and others. The first generation of CDs issued 1984 thru 1987 were the best by far. Now that digital playback technology has caught up to the silver discs, these albums sound very analogue-like.
CDs pressed in '84 and '85 mostly came from Germany and UK since the US pressing plants weren't up to speed yet. 

The Zeppelin CDs from Germany consistently had  higher quality sonics than the same albums pressed in the US and UK. These were early and 1st releases. Some Japanese releases were excellent as well, but were usually more detailed and not as musical. 
I grew up in the analogue days (vinyl and tape) so tape hiss is to be expected on recordings. In fact, it's a good sign that the music isn't overly compressed.

OTOH, there are many recordings from the 60s, 70s, and 80s that are of poor sound quality. These are the CDs that remastering was able to improve. Except for remastering performed during the Loudness Wars.

I have a lot of late 60's and on rock in the original vinyl. As time went on and my turntable wasn't hooked up I would buy the early CD releases of the same albums. What I noticed was the early CD releases from the mixed for vinyl masters were mostly horrible. When the same albums' remastered CD's were released I would buy those and for the most part they were pretty good. I especially liked the HDCD versions (I have a player that decodes them). I haven't delved into some of the other Hi-Rez formats so can't comment.

When redbook CD's were released from mixed for CD masters the quality was pretty good (until we got to the Loudness Wars as others have stated) and I think then you were looking for specific pressings, usually from different countries, (also, as others have pointed out). 

I think as time went on improvements in digital recording and playback equipment also played a significant role but I don't know of a specific time frame when there was a sea change that could be pointed to.

As @stilljim stated, some of the early US CDs were incorrectly mastered using the RIAA equalization for vinyl records. These CDs were pressed and sold by retailers. I believe these discs were recalled, but in any event, this hurt the public's experience with the new format.
These albums were then mastered and released using the proper EQ for the digital standard.