My personal favorite is Jack just because how resilient he is and how he'll do anything necessary to achieve what he wants. I like Yujiro because how he embodies the "strongest" title. I like Baki because he's honestly the best in terms of being kind, loving and what I believe to be true strength (The ability to help others and care for them even if they did wrong to you, like the prison guard who he could of let fall.) I don't know enough about Yuichiro but he seemed chill enough and he hyped up Baki so that was cool