At least traditionally, a hand-written note would be considered better because it is seen as more personal. Of course, this is a matter of opinion and people may no longer see things this way nearly as much since email and other electronic communications are becoming more and more common.
A hand-written communication is generally seen as the most intimate form of communication. It is seen as less formal than a typed communication because it actually has your personal handwriting. It is not just a generic message that could have been typed by anyone.
The more personal message is better for a thank you note. This is because gratitude is supposed to be a personal emotion. When you want to tell someone you are thankful, it is best to do so in a way that shows that you care enough to give it a personal touch.
The hand-written message is suggestive of a number of things:
- The person writing it exerts more effort into procuring an attractive card or note paper, a sign of caring for the recipient of the note.
- The writer of the hand-written message shows reciprocation for the recipient. The act is almost a quid pro quo--if this person has taken the time for me, I can take the time to write a thoughtful message.
- Handwriting lends a personal touch of itself because one's writing reveals much of one's character and personality.
- The hand-written note is something that can be kept as a reminder of the writer, and thus conveys more sentiment than an e-mail.