By “favorite fictional character” I don’t mean “favorite character of your favorite fiction”, consider the media itself to be irrelevant.
Just consider the character itself and how it changes throughout whichever segments of its timeline, regardless of how the world moves around it (unless it’s relevant);
the show / book / comic / game / political campaign itself may be absolute trash, but you love some character from that more than any other character from anything at all.
Like Magnifico from Wish, or the driver from Big Rigs: Over the Road Racing.
Commander Samuel Vimes, hands down.
His arc goes from zero to a million over the course of the Discworld series; even when he just has a slight Cameo he steals the scene because you get to see how terrified people are of him.
That’s the second mention from Discworld, I guess Pratchett really knew how to write his characters