I had a gigantic write-up back in that set review of how to analyze which one of these you should go with, and you should read that if youre looking for a more in-depth dive on the subject
Banlist History Restriction changes recorded for True Exodia
Vigilance How much does Summon: Yojimbo cost
If they wanted, they could look at the Future Future League results, try to pick the 15 most playable Standard cards, and stick them all at Mythic Rare
If a noncreature, nonland card is milled this way, create a Blood token
The reason is because the UW one feels like the default commander and White makes Allies the best for waterbending purposes, but Black offers some really powerful waterbending spells and more Clues for waterbending purposes