Hand written. A former major league player mentioned that to me in confidence several years ago. He would toss out typed requests and answer handwritten ones. Everyone's different, but you have a much better chance of success if it's hand written.
I have been told the same thing from a few NHL players but they do scan the letter to see if it is just a form letter or some real content and sign for real letters.
I have written all of the letters I have sent out.