First, lets cover definitions for both airspeeds:

1. Turbulence penetration airspeed (Vb) is the design speed for maximum gust intensity (i.e. the intersection between the 66 fps gust line and the maximum certified g load of the aircraft).
2. Maneuvering speed (Va) is defined as the speed at which the aircraft would reach its maximum positive load factor limit at the same time it would experience an aerodynamic stall.

After both definitions, shouldn't be more logical to fly in turbulent conditions at Va, since any encountered gust would give you maximum and equal margin from overstressing the airframe and stalling the aircraft?

For example, if turbulence penetration speed (Vb) is greater than Va for your specific aircraft, and you encounter severe turbulence while flying at Vb, that would mean that a potentially hazardous gust of wind would overstress the airframe first and therefore, not provide maximum protection from damaging the aircraft? On the other hand, if Vb is smaller than Va and assuming the same scenario as described above, you would first stall the aircraft (which again does not provide maximum protection in turbulence)?