Here's my take
A
Tangerine Dream - Phaedra, not familiar enough with the others except the first 3 albums which are interesting but not really A quality.
Lord Wind - Atlantean Monument, other albums don't matter that much
Kraftwerk - Trans Europe Express, not familiar enough their other albums to say.
Biosphere - Substrata
Beherit - EDS, H418ov21.C has cool ideas but is a bit of a mess.
Neptune Towers - both are good, but Caravans is better.
Steve Roach - Structures From Silence, Dreamtime Return, Midnight Moon, The Magnificent Void, other material is good but not as important.
Maeror Tri - Myein, other material is good but not as important. I would put The Beauty of Sadness in the B category.
Ildjarn-Nidhogg - Hardangervidda
Klaus Schulze - X
B+
Aphex Twin - Selected Ambient Works Volume II
Jean-Michel Jarre - Oxygene is solid, haven't heard anything else.
Endura - Everything, though Great God Pan is the jewel in the crown.
Tenhornedbeast - Hunts & Wars
Arktau Eos - Mirrorion, Ai Ma Ra
B and beyond (or rather below)
Myriads
I'm sure I missed something, but it seems like a decent list. if anyone wants me to go into greater detail on any particular albums, I will.