cheaper shipping Tag

We ship out a lot of items regularly - mostly that we have sold on eBay. Since our items are usually larger than 2lbs, we don't use the United States Postal Service (USPS) very much for shipping. We use either FedEx or UPS most of the time if we aren't shipping freight. FedEx and UPS are almost always going to be cheaper to use than USPS for something over 2lbs. But which is better to use for...