On time and willing to call before arrival to announce when they will arrive at your house. Delivery personnel are courteous and respectful of your home, efficient and usually quick to deliver salt to the softener.
I appreciate that you still have humans answering your phone; it's a lot simpler to deal with a person instead of having to wade through a phone tree to get to a person. I am fine with dealing with a recorded message for routine inquiries, but if I've got some sort of unusual situation, it needs a human.