Huge HUGE fan of both series, can't describe how much yakuza means to me. my life would not be complete without the series, my taste in a lot of stuff especially film has been altered heavily by the yakuza series.
Kuze is like, the whole reason I do what I do now, I wanted to see the films his actor Hitoshi Ozawa did and it led to me watching Bad City, then subscribing to his youtube channel, then looking at more movies because I was like "omg bad city was so good I gotta see more" and it led to me watching a ton of Japanese movies especially ones with other actors in the series and that led me (to better or for worse) doing a bunch of research on Japanese Cinema/Regular Cinema/Japanese Culture and all this other stuff. He's beyond my favorite character, he quite honestly changed my life inadvertently.
Outside of Kuze and some obvious picks like Kiryu or Majima I think my favorites would be Ichiban, Akiyama, and Saejima. I've been compared to Ichiban by my friends a bunch of times.
Stranger Than Heaven had me full on tweaking, losing my mind watching both trailers. I watched both repeatedly like a million times, I heard the song Ado and Snoop did for the trailer a million times, I was/still am beyond hyped for it. I wanna see this game come out. Like, badly.