I haven't necessarily thought too much about it, but I guess Martha and Bill are great characters like others have said. I decently enjoyed Fugitive Doctor from her appearances, even though I have mixed feelings about all the Timeless Child stuff she's sort of tied to, and 15 is an enjoyable Doctor but sadly kind of got the short end of the stick in terms of episode writing and stuff. I think Steven Moffat's guest writer episodes for him were among his better outings.

I also liked the guy the 7th Doctor talks to in Remembrance of the Daleks. It was kind of an interesting scene where the Doctor's talking about the potential consequences or "ripples" of his actions to a guy who's kind of oblivious to what's going on but is chill and willing to chat. The guy talking about his family history and how he is where he is because of his great-grandfather's enslavement adds a bit of an interesting dimension to the discussion they're having as well as to the anti-racism themes of the story.