In short; UPS and there various shipping methods.
On checkout you will be presented with everything from UPS Ground to UPS Next Day. However, the exact options available to you will depend on the shipping location and what UPS offers.
For “In Stock” items the order will ship UPS.
For “Factory Direct” items the order will most likely ship UPS. However some manufactures might ship an order through another carrier such as FedEx. Whichever shipping method you choose you will get the corresponding shipping service. For example if you choose UPS 3 Day Select and the manufacture decides to use FedEx, then your order would ship FedEx Express Saver, FedEx’s 3 day select equivalent.