Use Yours sincerely, (when you know the name of your addressee) and Yours faithfully, (when you’ve addressed it to “Dear Sir/Madam”) for very formal emails such as job applications.
Use Best regards, or Kind regards, in most other situations.
Even when writing to people you know well, it’s polite to sign off with something such as “All the best,” “Take care,” or “Have a nice day,” before typing your name.