Who to summon or grind for in Dokkan Battle

In a game with thousands of units, it can be hard to discern which are worth more of your time and resources aside from rarity. These two articles provide information about specific characters that will help you navigate the game with more ease. This game is all about playing smart, not hard, so informing yourself is hugely beneficial.
https://www.gamersdecide.com/articles/dokkan-battle-best-lr
https://www.gamersdecide.com/articles/dokkan-battle-best-characters