IMO, it's BLK regardless of the defense you play. I have always believed BLK is probably the most undervalued rating at all positions.
Don't equate the BLK rating just with shots blocked, it also has an effect on "altering shots," which means FG%. Zone defense gets more blocks than other defences, but that doesn't necessarily mean that BLK is more important in zone than other defenses.
ATH, SPD, DE, BLK, and ST all work together to determine defensive effectiveness (edit - along with RB of course - to minimize the other teams second chance points).
The order if importance of those ratings changes depending on position and the defense you play. SPD is more important than DE in press, and DE is more important than SPD in M2M. I have found BLK is as important as DE and SPD regardless of defense.
9/10/2010 3:12 PM (edited)