Currently, the branded returns portal only allows for one option for the shipping method.
Having only one option for the returns portal isn't a very cost-saving option for businesses. It may be easy for the customer, but the costs of shipping are only going up these days. Rather than trying to give the customer all kinds of options, why not just have the return shipment method default to the ground option of the carrier that it was originally shipped by?
So, if the package was shipped to the customer UPS, then the return label would be UPS Ground. If it was FedEx, then the return label would be FedEx Ground. Shipstation already has the original shipment information so, it doesn't seem like it would be too difficult to use the ground option of the original carrier as the default for the return label. In theory, this would be the best option for the business AND customer.