Speed / attack. Add some agi, if you feel that the beam torch is too difficult to use. Keep in mind that the agi doesn't remove the firing delay completely, but it does reduce it a noticeable amount.
When OS kicks in, you'll be focusing on spamming the beam torch while using it's insanely high speed to keep out of danger, making hp / def pretty pointless choices. And spec is sort of pointless since you'll rarely want to special with OS up.