What is best in a letter?

Depends on the type of letter you have in mind. Is it a formal or informally letter?

If you are applying for a job, then a typed letter would be a good idea. This also applies to letters to suppliers or people you do not know very well eg: to a shop or a business personnel etc.

A hand-written letter is more suitable if you are writing it to a family member, friends or close acquaintances or if a job advertisement stipulates they want their candidates to submit a hand written application then you can do without typing the letter.

I prefer to type all my letters out as I’m rather lazy when it comes to double checking my spelling errors and with handwritten letter, I have to spend time proof reading which mean time wasting. If the letter is too someone close, I usually change the font to a style which is funky and italics.