I have Prime and would not be without it.
Both UPS and FEDEX have joint shipping programs with the USPS were the initial shipment is with one of the private carriers and then they hand the package off to the USPS at the local post office for final delivery. I believe there is a fairly low weight limit but not sure of that. We actually get delivery on Sunday from USPS--something I try to avoid by opting for longer delivery times but my wife is not as "carbon sensitive".
I would prefer the USPS not be involved since our local service is deplorable. Both UPS and FEDEX put packages in the garage, out of the weather and out of sight. I have had USPS packages actually placed in the middle of the lane. A few weeks ago they forced a package in the mail box that almost fit, I had to cut a hole in the end of the box to put my finger inside to pull it back out.
Other than our local USPS problems, the joint arrangement seems to make a lot of sense.
"A pessimist sees the difficulty in every opportunity, an optimist sees the opportunity in every difficulty” ---Sir Winston Churchill
"Political extremism involves two prime ingredients: an excessively simple diagnosis of the world's ills, and a conviction that there are identifiable villains back of it all." ---John W. Gardner
“You can’t go back and change the beginning, but you can start where you are and change the ending.” ---C. S. Lewis