[atomi]

It's possible that the quality of service you get from USPS correlates to the city it's operating from. I prefer USPS in my area. Their delivery schedule is consistent. In contrast, UPS will sometimes show up in the morning or as late in the evening as 9 PM and rescheduled deliveries are too commom.

[tjl]

UPS has a habit of just leaving a "sorry I missed you" sheet at my building. Several times, I've been home the entire day the delivery happened, but they never buzzed my apartment. They just left without contacting me and saying that I wasn't home as the reason.

[mixmastamyk]

USPS will often have better access to your building and/or leave small packages in the mailbox, which I appreciate.