Use BT on cooldown unless you're finishing off your 3 Bloodsurge proc's.
So if both are procc'd and you BT is off cd, it'll look like this: BT>RB>WS>WS>WS>BT...
but if you BT is on CD, then you're going to have a rotation like this: RB>BT>WS>WS>WS>BT...
This is really situational and really depends on how much rage you're gaining at that particular time. If you cant burn it off fast enough, use WS but if you're trying to be rage conscious then use HT>BS.