There are many ways to close a personal letter. The closing that you use depends on the person that you are writing to. If you are writing a letter to a family member or a close friend then love would be appropriate. If you are writing to a new friend sincerely or fondest regards would be okay. If you are writing to a casual acquaintance then sincerely would definitely be in order. If you are
. writing a business acquaintance then thank you is probably best. The trick is to make the closing fit the person you are writing to.