Genesis
King Crimson
Yes
If this were, say, 40 years earlier, i could probably fill out a top 15 or more. But those three dominate my prog rock tastes nowadays.
For Genesis, the meat begins with Nursery Cryme and lasts through The Lamb but i also like the earlier Trespass and first two post-Gabriel albums, Trick of the Tail and Wind & Wuthering.
For Crimson, In the Court but primarily for the amazing '73 - '74 band with Larks' Tongues, Starless... and Red. Plus assorted live recordings from the period.
For Yes, it's their primo '70s period starting with The Yes Album and lasting through about half of Tales... and part of Relayer, even some of Going for the One.
I am also still into Floyd but more selectively, with their mid '70s albums and some of the early Sid work from the '60s.
I was hugely into Tull and ELP in the '70s. Can't stand ELP now but i still enjoy some Tull.
Focus' Live at the Rainbow holds up very well for me. I never cared for Rush back then but now i enjoy a bunch of their songs.