E-Mail or Handwritten Thank you

I had a phone interview two days ago that I think went well. I want to send a thank you, but I don't know which route to go. Everything so far has been electronic and phone, but something handwritten seems to say a bit more than an e-mail. If I go handwritten, is something like a thank you card from Hallmark appropriate, or keep it simple with the note on a piece of paper?

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