So there are many actors who have been Doctor Who and Harry Potter, and there are many that I love, but I have to say my favorite would have to be Warwick Davis. I have always loved him since I was a little kid. He is just a really wonderful person and actor. I enjoy him in everything he is in.
He played Professor Flitwick and the goblin Griphook, in the Harry Potter movies, and he played Porridge in the Series 7 Doctor Who episode "Nightmare In Silver".