Original Message

First off Vtoss is strictly a twin engine term. It's the speed at which you have single engine fly away power to continue to accelerate to VY. Vtoss is on the back side of the power curve below VY so it's not the most efficient speed. Vtoss is not a speed isually intended to linger at unless first segment climb procedures specify vtoss as a procedural speed until obstacle clearance. Think of it as a marker for single engine fly away capability to transtition to VY or greater. Below Vtoss single engine fly away is not guaranteed considering your AGL height. 

VY is best rate of climb as we all know, least drag etc. In all helicopters VY is the bottom of the power curve. Always and forever.

If you want obstacle clearance VY is your best bet, or consider a speed between Vtoss and VY for obstacle clearance.

Technically speaking VX, or best angle, in a helicopter is straight up...