the history of middle earth. I just bought the first 6 editions in paperback from Del Rey/Ballantine books.
These are basically the same as the Harper Collins printings.

The first book was begun during WW1 the Book of Lost tales. I’ve always enjoyed the first version of Tinuviel aka the story of Beren and Luthien. The early version of Turin Turambar and the dragon. Tolkien’s early poetry and verse. I also like the poetic Lays of Beleriand versions, and the lost road time travel story that is a flashback to the Fall of Numenor.