you have many choices, why do you think only about ninja ninja ninja?!!!!!!!!!!!!!!!!!!!!!!
lets think about ninja warrior fire: you need good gears to be able to fight well, it is disadvantage if I am fighting with trojan or warrior I should keep my health full all the time, Iam not sure how he will hit me the next time, but if I am fighting with fire I am sure he will hit me with legal number so that I know when should I cure, you need good gears, fires has low defence, it is hard to level up fire or train it is skills, you should have fixed phoenix, fire has no way to get money easily, only for DB bulkers, but who can play with fire well will be the best.
about ninja ninja ninja: I don't like that character, it has low def and HP so it will die only one hit, needs lots of stamina, it is hard to get it while fighting, but when it hits character then this character is DEAD!!!
ninja warrior trojan: It has high attack, medium def. fire can kill them easily unless they are good enough in SS and FB
ninja warrior warrior: I am gonna make that character, but not lots fo people like it, warrior is characterized by VERY high defence it is attack less than medium with a bit.
ninja trojan archer, it is the best combo for an archer if you like archers then do it, I don't think this combo will help you to kill your enemies but it will help you to make them avoid you, they will run during fighting.
I am sorry if I increased the choices and made it for you hard to think between all these characters, but I was just showing you all characters, I hope you choose the best and become the strongest.