Sincerely, Regards, Yours truly, and Yours sincerely - These are the simplest and most useful letter closings to use in a formal business setting.
Best regards, Cordially, and Yours respectfully - These letter closings fill the need for something slightly more personal. They are appropriate once you have some knowledge of the person to whom you are writing. You may have corresponded via email a few times, had a face-to-face or phone interview, or met at a networking event.
Warm regards, Best wishes, and With appreciation - These letter closings are also appropriate once you have some knowledge or connection to the person to whom you are writing. Because they can relate back to the content of the letter, they can give closure to the point of the letter. Only use these if they make sense with the content of your letter.
This is from how to end a letter by the balance.