Koyasan or Nachi falls

Hello, I'm planning my first trip to Japan and I have one day free between Osaka and Kyoto, my first plan was to go early in the morning to Mount Koya from Osaka and spend the night in a temple and go to Kyoto in the morning of next day but Nachi falls is something I also want to see but I can only do one of them, I don't know which one is more beautiful, also if possible I'd like to get to Kyoto by evening of the next day, I'd like to hear recommendations from people that have gone to one of them or both of them, thank you

Koyasan would be much easier as a single day.