This depends on the position players would like to slot in, either Kaeya or Chongyun, since Kaeya can be both Main DPS and Sub DPS while offering an exploration boost through the stamina conservation talent and longer-lasting ice bridges. He is pretty reliable since he feels like an all-rounder. Chongyun has more significant potential to be a Main DPS and allow better Freeze or Melt comps since his elemental mastery is higher. I love using Kaeya, and I feel like he is capable of doing what I expect out of a Cryo supplier in my team. If Freeze is what you are going for, I would recommend Kaeya. If Shatter damage is what you are going for, I would suggest Chongyun.