Priority in Priority Mail is a joke during the holiday season!
FedEx and UPS are the best way to go, but USPS is cheapest on fast delivery.
Go to USPS.com and calculate the post. You will see Express mail. Click onthat overnight link. It will tell you about commitments. Plug in the origin/dest. zipcode and ship date. It will give you a new page with pretty accurate delivery times depending on which post office you drop off the package at.
I don't really ship that many Express Mail items, but I believe all of them got their overnight. Had a few that said resident not at home etc.
I shipped 2 or 3 express mail packages the 2nd half of this December and all of them were shipped overnight.