My favorite actress changes a lot. Right now it's probably Mila Kunis, because she just seems so likable. I thought she was great in both Black Swan and Friends With Benefits (which was WAY better than the similar Natalie Portman/Ashton Kutcher one).
I used to like Zooey Deschanel a lot but I've gotten sort of tired of her and have begun to find her annoying.
As for actors, I've got eyes on Jake Gyllenhaal and think Robert Downy Jr is pretty great. Ryan Gosling has a pretty solid record of good movies and interesting character choices as well.
Sorry I'm indecisive lol