alt Hacker NewsA lot of that uncertainty has to do with USPS, who keeps getting slower, and their delivery date estimates are at this point often 2-3 days more optimistic than reality.
At least in my experience, UPS, Fedex, etc., tend to deliver when the estimate says.
For me, FedEx is almost always a day or two over the initial estimate, and the package looks like it's been routed through a war zone.
UPS is generally pretty good.