I do prefer recasting, but I had Bewitched as my prime example of switching actors midstream, granted with an adult character, to inform my tastes. And all the soap operas on Day Time TV.

Worst casting of an actor to a role is harder for me to pinpoint. I mean, the actor that was playing Mat in Wheel of Time didn't seem to be forming the right chemistry with the rest of the cast, but for whatever reasons, he was replaced for the upcoming season. I don't do the books, so I can't say if it was poor casting to the role, or just actor differences throwing me that vibe.

I've got some actors I never gel to no matter the role, but I honestly cannot think of a role where I feel like a different actor would have made much of a difference.