We have been using ShipWorks for 14 years. It allows us to ship hundreds of orders fast and with accuracy. Shipworks interface allows us to ship using several different options, comparing prices and estimated delivery times quickly and easily. We have stores on several different platforms and Shipworks allows us to download them into their one interface, and ship them from one central place.
Shipworks customer service/support people have always been fast and knowledgeable.
Shipworks is always issuing [free] upgrades, keeping up with new technologies, marketplaces, shipping options, etc.