Phase- In some ways, the more primitive the recording equipment the better the sound: the material just leaps out of the grooves without a hint of stridency. Some examples: the very first pressings of Alice Cooper's Love it to Death on the pink Straight label have an immediacy that is lost on even the earliest Warner green label pressings that are maybe 6 months later.
The first pressings of Neil Young's Harvest, with the textured cover- has an intimacy that is lost on all the remasters I have heard, although the Chris Bellman recut is very good and has quieter surfaces.
All of those wonderful UK Vertigos- I came to that party a little late, and yes they are now pricey, but the self-titled May Blitz album is a deadly combination of biting psychedelic guitars that have harmonic overtones and the overall record has enormous punch.
Early pressings of Three Dog Night's album with the song 'One' (if you can find a pressing that doesn't have the hype sticker, all the better). Crazy good sound on a record that probably costs 15 bucks for a M- copy on E-bay.
The 'RL' cut of LZII is no secret and fetches big money, but it has a freight train delivery on many tracks.
Janis Ian's Between the Lines- standard issue Columbia pressing -a 15 or 20 dollar record, used, sounds much more vivid than the Boxstar reissue.
Early (Shelter) pressings of the Phoebe Snow record are also fantastic sounding.
The Green label pressings of several early Van Morrison records- extremely good, not terribly pricey.
With the exception of the 'RL' Zep and the Vertigos, none of these are big money. I could go on, but most of these are pretty thoroughly discussed elsewhere on the web. (However, nobody was onto that pink label pressing of the Alice Cooper record as far as I could tell- I bought my first copy largely because I wanted an early pressing and didn't appreciate how much better it was than the Green Label copies until I started to compare them- so now, I have about a dozen copies, all early, including a WLP of the pink Straight label pressing).
I don't necessarily buy 'by label' but I've now managed to fill in a lot of my early hard rock/pysch records with early UK Harvest, Island pink label and more Vertigos than I'd care to admit. All of these were pressed in the late 60's and early 70's.
FWIW, out of the many pressings of Dark Side that I have, the best to my ears is UK A3/B3.
And I sold a UHQR of Tea for the Tillerman that I bought new, back in the day, after buying an old Island pink that simply sounded more like real music.