It's not even a choice mate. One's a mortal theater performer while the other is a freaking immortal Radish GOD. Nahida all the way. I'd even say she's a must but beating the game's content doesn't really require specific characters. However, Nahida is a solid SSS for Exploration and Dendro Apication. With a good artifact set that maximizes EM (Elemental Mastery), she can mow down crowds of enemies with such ease, you practically can kill a hilichurl from up a ledge without needing to climb up and melee or even snipe them from faraway. That and the mind reading gimmick she does on Sumeru just straight up gave her "Most Powerful and Adorable"Archon status.
