Each equipment has its own rarity, that is displayed as a number on top-right of the NFT
You can check the rarity tier below:
Mythical (5) > Legendary (4) > Epic (3) > Rare (2) > Common (1) > Basic (0)
As you can see, the Mythical has the rarity number 5, so its the better card in the game.
On the other hand, the Basic ones has the rarity number 0 so its the cheapeast choice for new entrants but has the worst mining power of all.