What is the difference between regular postal delivery and private courier delivery?

Question

what is the difference between regular U.S. postal delivery service and private courier (non-USPS) deliveries? I want to send a document with a more secure and fast way...which one should i choose? and these two deliveries are with the different address. please give some help. thanks

Answer 1

USPS is best

there are lost of peers in private DHL etc., who are also reliable.