3BB has a couple advantages over 66B that frame data doesn't tell you. The biggest reason is because 3BB can hit the ground and 66B can't. Another thing is that, while according to the frame data 66B is faster, unless you buffer it from something this isn't the case because 3BB is a single input command and 66B is a two input command. Plus, I figured I generally wouldn't get punished on block for doing 3BB and it is one of Algol's only moves that damages the guard gauge heavily. Overall I certainly consider 66B the better move but 3BB is not without it's perks.