Best regards, Best wishes and Kindest regards are considered as a semi-formal, but respectful sign-offs. They are not as formal as Yours sincerely, but they can be used in business letters.
- Best regards - is a semi-formal, friendly, but respectful closing for letters or emails. It can be used for both, personal and peofessional correspondence.
- Kindest regards - is a bit more formal sign-off than best regards.
- Best wishes - is a bit less formal sign-off than best regards.