I just finished the newest chapter >:DD
As for what weapon?
It depends on a few factors, being our skills, species, and what we're comfortable with! Taking Mikey for an example, he's a box turtle, which are usually more flexible due to their plastrons top center. The top center is a flexible hinge that usually allows the front and rear of the lower shell to press against the upper shell, which just means he's flexible. Mikey has also practiced his acrobatics, and other stuff which adds to his skill set! Making a kusari fundō a perfect weapon for him, as it combines flexibility and striking power into a singular weapon.
Another example, Donnie. He's a softshell turtle, which are somewhat flexible, but sense Donnie isn't comfortable with being vulnerable, he has his battle shell. His weapon, the bō staff is perfect for flexibility, striking power, thrusting, poking and keeping your opponent at a distance. Which is also a good weapon for Donnie!
So to sum it up, it really depends on species, skills, and comfortability! If you need any help with picking a turtle species, weapon, or making a skill set for our main character I can help >:3