I do love me some Orson Welles, early and often. Favorite performances and movies are a little hard to choose. I love whichever one I'm watching. But let's try.
First, his own films. Actually, Kane and Ambersons are so obvious that those will go without saying and I shall pick and choose from the rest. The Stranger, Touch of Evil, Chimes at Midnight, and The Trial. With an Oxford Comma. So, does this mean I don't like the other Shakespeare films or F for Fake or Lady from Shanghai or Mr. Arkadin or something else I might be forgetting? Of course not. I love 'em all. But I'm particularly enamored of those above, and of his own performances in every last one of his films.
Performances in other works: The Third Man, Jane Eyre, Return to Glennascaul, Catch-22, History of the World, Part I (narrator). Also, I only saw it when broadcast in 1972, but I always remembered loving his genius at milking every line in the Hallmark TV production of The Man Who Came to Dinner. But his appearances and narrations are always a gift.
And then of course there are the radio programs. I love it all.