Difficult to decide. All the Blue Note Classics/Reissue Series were fine. Great music, a lot of it previously unheard, nicely produced (except for the odd one which was unreadable(was it a Chick Core with yellow print on beige). Good essays too.
"High Step", "Back From The Gig", "One For One", "The Procrastinator", "Here To Stay" all come to mind as being a bit special. I still have a few.