I don't know who's good, help me

If it's within the range that's written, Mountain is the only choice. It's Star 6, so gathering育成 materials will be tough, but good luck!

If you have the Sivilight Eterna, I don't think you're a beginner, so I'd recommend Schwartzkaiser, Astegine, Horn, and Pepe. It's good to focus on developing parts that feel lacking among the characters you're already raising.

Mountain's S2 skill is incredibly strong in the current meta~! I think it's an excellent operator that can do both offense and tanking👍 I can't give the best advice since I'm missing a lot of characters, but I think just promoting Mountain to Elite 1 would be good~!! Personally, he's an operator worthy of the Hall of Fame!

Considering examples not mentioned above, I'd like to recommend Chen. As a swordmaster, she's designed as a vanguard who can endure to some extent with a block count of 2. Her special traits include attack recovery, damage taken recovery, and SP replenishment. In situations where skills can't be completed without enemies, like with Thorns, she has significant value. If your main heavy defender is Mudrock, she also has a damage taken recovery skill. Using them together allows for skill chaining, potentially leading to overwhelming power, and if Chen finishes off any missed enemies, there will be fewer openings.