I'm noticing that agility helps out a lot on O linemen with blocking. Strength is first, and blocking is very good, but you need speed to get to your spots and agility/vision to get to the best blocking position. However, agility helps with the actual block, while vision does not. Confidence also helps, but that generally helps every position.
I would go: strength, agility, blocking, speed, vision, confidence/stamina (with majors getting +1 for build purposes)
For run blocking O-linemen this would become: strength, blocking, agility, vision, speed, confidence, stamina
For pass blocking O-linemen this becomes: agility, blocking, strength, vision, speed, confidence, stamina (LOTs, IMO)