It'd definitely be Troy or Daniel. Really, really great characters and every time they're on-screen it just makes the scene so much better. Troy is one of the reasons I'd rewatch S3 over and over again and Daniel is just amazing. I really hope the latter doesn't disappear at the end of S5 because he's one of the few characters I care about, plus his and Dwight's friendship is one I didn't see coming but I'm happy we have it. John, Sarah, and Dwight are my other favorite characters as well.