Handwritten letters are a must if you want to signal high personal involvement, for example

• proposing marriage, reconciliation, divorce
• offering advice in existential crises
• condoling in tragic cases
• excusing yourself for serious offences
• etc.

Always use a fountain pen - a cheap one will do. Always design your letter on your computer first. If you do not trust your handwriting to look good, print the letter twice, with hyphenation but no right-justification, using a large font that resembles handwriting. Position one of the printouts under your letter paper so that it shines through (however faintly), and trace it approximately, in your best own handwriting.

Letters from famous writers fetch high prices at auction. Just imagine how rich you can make the recipients ... ;)