I would go hydro pump. 80% accuracy is still high and it doesn't have a too terribly chance of missing. If you are really worried about the miss go with surf. It is kind of opinionated because either is still good.
Secret sword is preferred as it hits Pokemon who are special walls on their physical defensive side. But if you are talking about sacred sword, it is a physical move and keldeo has higher special attack. Go with focus blast. Secret sword is still better, though.