Its hard to choose a favorite character because there are so many characters in the series, but if I had to I would choose Chizome or Shigaraki. I like Chizome because of his beliefs and I like Shigaraki because of his quirk and how powerful he was/is.
My favorite quirk though is Overclock because of the potential it has to become the strongest quirk in the series, but because it isn't really strong at the moment then I would probably say All for one or Foresight because they are cool XD.
Heres a link to a thread i made a few days ago about Overclock if you want to read about it. There are some things that i want to add to the thread but too lazy to do so XD.
https://animebase.me/threads/overclock-vs-other-quirks-new-best-quirk.770868/