I like USPS. Even if sometimes, personal letters may take a while to send over. I prefer it over UPS because I don't have to sign anything and they'll drop it off into my mailbox or on my front porch for me to pick up later.
Those free flat rate boxes and envelopes are great. Who doesn't like free shipping materials? My problem is most of the things I sell are either too big or too small to fit in them. I don't use them much because it is usually cheaper for the customer to ship first class.
Extreme loathing, that's my initial response when I hear 'USPS'. I had a priority mail package, which is supposed to take 1-3 days, take a full 7 days to get to my home from New York to Georgia. I get stuff from all over the US with Priority and it almost never takes more than 2. I could have gotten first class mail for much cheaper and got it in the same amount of time, or less. Right now I have another package from New York on its way first class. I bought it on the 8th, The post office accepted it on the 9th, and the tracking didn't update at all until last night, the 12th. It's still in New York, by the way. I don't know if I can really blame the USPS, though. It's really just that hub and it's because they recently had a sorting facility shut down which has just confused everything.
The closing and reshuffling of processing centers is causing some problems all over the country as workers adjust to increased workload, new zip codes and such. The estimated arrival on U.S. mail are just that, an estimate. A lot of people think they are guarantees, but the only guaranteed mail is Express, which is very expensive. I believe the post office actually has by code 30 days to deliver a priority item.
I am a long time eBay seller and instructor. I prefer the post office. Most buyers will want priority mail because they want their stuff pronto! The problem with your tracking number with the USPS is you usually don't get your info until the package or mailing has arrived.
I havent ran into any problems with USPS yet but I'd always like a tracking number just to be safe incase something does go wrong. With heavy items i'd worry about USPS because they tend to lose big things easier than smaller things (go figure). Just from my personal experience though.
Personally, I prefer the USPS. They make more of an effort to get your packages delivered to you. If there is the chance that they can't deliver it to you at your home, there are more post offices than there are UPS depots, so you can easily pick up your package. I've seen too much slip shod work from UPS guys to ever hope for the demise of the USPS. Although, it looks like it will be harder and harder for the USPS to survive.
USPS is really hamstrung by not being allowed to set prices that would insure enough revenue. I read recently that it costs 71 cents to process a 1 oz. first class letter. However, the post office has to get congressional approval to raise rates. Constituents would cry bloody murder if the post office nearly doubled the cost of stamps.
It's my least favorite because the shipping and tracking is not reliable. I purchased delivery confirmation and didn't even receive an email when a package was delivered to a customer. The only think I like about USPS that they ships books really cheap (regardless of weight) and they deliver the mail in my area early. With UPS and Fedex I usually have to wait until the evening to get packages.
If I am selling an item I always get a tracking number unless it is someone I know. Without this, I am liable for the package, plus it is better assurance to have this when you are working with PayPal or other payment platforms.