I don't mean to be that guy because I'm usually not but some people don't understand that interludes are not instrumentals. If you don't believe me you can look i up
I'd say a tie between Session and Jornada del Muerto with The Requiem coming in at a close second. Yes I know Jornada isn't a true instrumental, DEAL WITH IT.
Now that I think more about it, I probably like A.six (long version), program and the bonus instrumental on HTEP as much as Session. Pale, Lockjaw, Annoucment service Public, and The Requiem are really close too. Lp instrumentals are such great tracks!