I use USPS mainly for the ease of use and because EVERYONE deals with the post office. I send all my packages via USPS first class mail and I usually ship within 24 hrs, 6 days a week. I also always get delivery confirmation so that there is a tracking option to see the progress and state of the package. I also offer USPS Priority mail 2-3 day service. I found out the hard way one time that even though you are paying for a faster shipping method, Priority DOES NOT guarantee delivery in that time frame. It is a service for faster delivery but without a promise to be there. If you want a guarantee you must use Express mail. Post office delays are inevitable, machines, car, plane issues and weather are the most common and that doesn't account for human error but I think for the price and options USPS is the best choice. UPS and FedEX are not very cost effective for a small business let alone a sole crafter selling her items for extra craft cash.
Once an item has left the sellers hands it then becomes the shippers responsibility but remember they DO NOT promise anything unless you pay for it. Express has that higher price tag and a promise of delivery buy a certain time. You can also buy insurance on the item to protect against damage or loss, promising some restitution.
Most shops have these standard policies for the shipping of items along with letting you know that they DO NOT offer any refund of items lost or delayed as well as not refunding the shipping cost of returned/exchanged items.
I go above and beyond to make my customers happy so if there is something special you need, a custom item or special shipping and handling just ask, I will try my best to make or get you what you need. Happy Shopping!