Interesting.
In my particular case it was FedEx/Smartpost. In my area, the USPS leg has been very reliable, 100% next day delivery from drop off at their Springfield, MA center to my door in Albany NY.
The FedEx Ground leg took forever, my little box made like 4 stops in Ohio and PA before hitting the post office in MA.
UPS typically does that in 2-3 days, USPS typically 3.
Strange. In Austria, things shipped within 24h of ordering, mostly. UPS/DHL within 48h, but mostly less. They ramp up capacity a lot during holiday season.
They even delivered on sundays this year, which is pretty much unheard of in Austria.
Source: I work for an online retailer.