Either Shunsui, atau Jushiro. I really like them both, because, even though they are the oldest Captains (as well as Unohana) and have been there since Yama-ji became Captain-Commander, they still follow their own idea of justice, which was interesting. Even though they were going against the Gotei 13, they still believed Rukia to be innocent and went against their Sensei in order to try and save her and assist the Ryoka.
My opinion isn't often shared, mainly because most people view him as a pseudovillain, but that's just what makes Kurotsuchi Mayuri so amazing. He's not the quintessential heroic figure to any extent, and he defies a number of tropes. I like the fact that his fights don't simply come down to who is the strongest, that he rarely holds back as so many other captains do, and he has one of the most interesting looks among them.
Mayuri Kurosutchi. I like unique, kind of odd characters.. and he's a jerk which is why he's freaking hilarious. I can't help but laugh when he comes on the screen... and one lebih thing, his long speech on perfection was beyond epic.