371 Four-Part Chorales (BWV 253-438 and others) - Breitkopf Urtext - organ (piano or harpsichord) - (EB 8610)

I'm not sure who the intended audience is for this. It's comprehensive and (I would imagine) accurate enough to use as a study score, but four-part open score would work better for that application. For a performer, some of the pieces are typeset far too compactly to be readable, unless you've got exceptional eyesight. Personally, I don't really like the landscape layout for music, but I guess it allows the page count to be kept manageable. My search for the ideal chorale book continues.