To take it one step further from Pegasus77, once clear of obstacles, Vy is definately the preferred option in terms of time, fuel, and cost. You will reach Cruise Altitude faster, and therefore use less fuel to get there, and, as Vy is a higher speed than Vx, cover a greater distance in that lesser time. Overall sector time will therefore be reduced, and fuel used will be less, both saving cost.
I presume that we're talking piston engines here, and a third benefit of climbing at the higher Vy speed will be reduced Cylinder Head Temperatures. That's a cost savings in the long run too.
Regards,
Old Smokey