… FedEx, according to ShipMatrix, a shipping operations software company.
Here are …
Dec. 14: FedEx Ground and Freight
Dec. 16: USPS Priority Mail … FedEx Express Saver and 3Day Freight, UPS 3 Day Select
Dec … Air 
Dec. 22: FedEx 1Day Freight, UPS Next Day Air 
Dec …
When to mail gifts for Christmas? Busiest shipping week is here.