I went with vortech because...
like mentioned earlier - heat soak. no exhaust side so no exhaust. i can put my hand on my charger i have driven and it won't burn my hand.
second my charger is 73% effiecent, which is more effiecent and a roots or screw could ever hope to be.
yes there is lag just like a turbo but if you are wanting to make 400hp a centrifigual is much more realistic because it can spool to over 20psi, also previously stated. but where it does have the advantage over a turbo is that i start bulding boost at 2k rpm with 6k to go. if i was running 20psi at 2k i would be at something lke 5-7psi already and you would be pulling a turbo car.
i only run 7-8psi so at 2k im at about 3psi so at low boost levels turbo is the way to go because it is much more effiecent.