Cube Sales or Miracle Time?

I'm wondering which would be more worth it.

Firstly, I strongly prefer to use Super Miracle Cubes because they can upgrade an item to Legendary, and has more chance of upgrading tiers, so I probably won't be buying the Miracle Cube sales later.

So, I'm wondering whether to buy Super Miracle Cubes when they're on sale, or buy them at regular price during a Miracle Time and use them.

Thanks for help