I'm just guessin here but I have always heard the centrifugal blowers were more efficient, built less heat per lb of boost which = more power.

My guess would be you'd make more peak power with the centrifugal but you'd make a lot more torque and power right off the bat with the roots.

I have always wondered this myself though. I have seen many debates between centrifugal blowers and hybrid roots/twin screws, but my guess is a plain old roots would be the most inefficient (??)