Hey gang. Not claiming guru status on these- just my experience when I waded into the mix some time ago. My personal favorite is the band's first album, and there, I must have a dozen different copies, including a Classic 45. My preferred is a second Japan press, which wasn't big money. The SH forum fav is easily look-able there (it's a Piros cut).
@slaw- don't hate the Classic, bought them as they were released for the most part. They sound more "audiophile," somewhat "tipped up" on top (BG characteristic to me) and far more "detail" but lacking overall cohesiveness or balance. The older cuts just work better to my ears.
On III, the early Peter Grant UK is the one.
@tablejockey - never saw that record in the wild. Those Haeco -CSG records were odd ducks, sonically. Cream's Wheels of Fire was cut using the process. I don't think it can be undone.
My favorite oddity, which I do not own-- is In the Court of the Crimson King as a Vertigo Swirl. Never saw one of those in the wild either. Curiosity piece more than anything.
Have fun!