I would like 3 disc album. This would be my perfect (and possible, because they will not release all unreleased songs at once, of course) release:
First disc - Bad (original 1987 release) + Leave Me Alone.
Second disc - all songs from Bad era (already released and few unreleased, with demos and early versions of some songs, like TUC). It would be nice to have Streetwalker, Todo Mi Amor Eres Tu, Fly Away, Scared of the Moon, We Are Here to Change the World, Cheater & Come Together (Moonwalker version, previously released on Remember the Time single) all on one album. Of course with 2-3 "new" previuosly unreleased tracks from Bad sessions (Groove of Midnight...) along with demos and early versions of Smooth Criminal (Chicago 1945, Al Capone), The Way You Make Me Feel (Hot Fever) and Liberian Girl (Pyramid Girl). Previously unreleased French version of I Just Can't Stop Loving You would be nice too.
Third disc would be DVD live from Bad World Tour Wembley '88.