Hm...Decided to just do an actual list of my favourite characters.
Endeavour is my current favourite. The moment that solidifed this was his battle with AFO. His realization that his attempts at redemption and atonement were ultimately worthless, and the only thing he could do that could give his life meaning was struggle endlessly against his own weakness is for me the most peak shit in the entire series. It breaks the mould for the typical "character getting redemption" or "character overcoming their flaw" story arc in a really interesting way, with Endeavour's ultimate redemption not being presented as actually possible through any single symbolic act, but through a continuous, never ending struggle against his personal insecurities. Very much a break from the typical escapist forms of character development.
Next is Kirishima. Kirishima became my boy in Overhaul, and he has a very similar character struggle with Endeavour, in the sense that he is someone who must consistently struggle against his own insecurities, and even by the end of the Overhaul arc, he still didn't feel like he had actually overcome his insecurities.
This is a surprising one, but I really vibe with Jiro. Jiro for me, had the best character arc of the female cast. She isn't as cool as any of the male cast members that are typically considered the heavy hitters of the series, but her arc is very grounded in high school insecurity, with her conflict coming from being embarrassed by her hobby due to giving up on that career path for another one. Its a classic "thing I love" versus "thing I actually want to be" sort of growing up struggle. I think her finding affirmation and self confidence in her performing in the culture festival is one of my favourite moments in the series. Not to mention, I enjoy pretty much all her moments after that, from her nice moment with Kaminari in the first war, to her speech in chapter 327, and I'm really happy she's having a pretty much role in the final arc of this series.