Call me sentimental, but I like getting my mail everyday. I try to ship everything I can USPS to support those folks. Hard working bunch of people.
I really like those boxes they have that if it fits it ships at one price, regardless of weight (max 70 lbs).
Edit: I also like they will come to my place to pick up the package and offer the same timeframe delivery options as the private companies.
I used to use Priority Mail exclusively as no matter where I shipped my frozen fish in insulated boxes in the U.S., including Hawaii; it got there in three days. And it was a better rate than UPS and Fed Ex The last two out of three boxes I shipped to Northwest Ohio from Northeast indiana took four days. I can drive their in two hours. The second one I shipped 2nd day and it still took 4 days! It was explained to me that every parcel in Indiana regardless of where it goes has to be sorted in Indianapolis now. They lost me as a customer.