It depends, a bit, what your fitness goals are.
If you're doing squats because you want to be able to lift 100 lbs boxes confidently, or boxing because you want to fistfight in the real world, you might be limited by the fact VR can't provide resistance; detect if you're putting enough force in; or punch back.
On the other hand, if you're looking to get your heart and lungs going, burn some calories, and generally compensate for the fact you've been sitting at a desk all day? Anything from ballet to bodybuilding will do, including VR exercise.
