Which scenario would be best for the world?
China as the worlds superpower? US? Russia?
Or, a vacuum where no one country could claim the title?
balances of power have historically lead a to a greater chance of major war. Both World Wars, the Franco Prussian War, the Crimean War, the Napoleonic wars, the world wide conflict that grew out of the American Revolution and the seven years war all came about when there was relative parity between groups of nations. Nuclear weapons may have changed the equation (they certainly seem to restrict any potential conflict between the Warsaw Pact and Nato), but I would prefer not to chance it.
Fwiw though, China is still 20 years or more away from being a Superpower. They are a regional power to be sure, but their ability to impact events outside of their region is limited, at least in terms of conventional warfare.