I feel compelled to chime in on this one. I agree 100% with the necessity to build core strength, use the legs, proper mechanics, etc. But that is not going to effect bat speed...not completely, anyway. I feel the greatest impact on bat speed happens in a very narrow window in the swing process. Specifically, between contact and extension. It's the release of the power that the hitter has collected up to that point that must happen in a very specific time in the swing in order to create the most impact. It must happen very quick because, obviously, there is a very short window of opportunity to put all that power to the pitched ball. All that other stuff (timing, legs, hips, weight shift) is equally important to assure that power goes through the pitch, but for the specific question of bat speed I vote for strong hands whipping that bat at contact through extension.