I really like pretty much the entire cast in Stormlight, it's a bit hard to pick. As of where I am in RoW (just starting on part 3) I think it's a tie between Shallan, Pattern, and Syl, but all that will probably change depending on the day you ask me
Probably The Emperor's Soul. I absolutely love the long series, but on an individual book level I just feel like Emperor's Soul is just does so much so well for such a short book, and the idea of Forgery as a magic system is extremely fascinating to me.
The Witcher short stories are where I started off getting into fantasy due to the games (I haven't gotten around to the novels yet), and then I moved on to Kingkiller. After that is when I started Mistborn and really got into the Cosmere. Like I mentioned, I've also very slowly been working my way through WoT, but it hasn't been my main focus because it's such a long series and I don't want it to completely take over my life (yet). Next on my plate after RoW and finishing the next book or two in WoT I'm looking to start on either First Law or Malazan.