ShipStation

This is the 3rd shipping platform I've used with Shopify. ShipStation is by far the best. All of the big shipping platforms contract for very similar rates, so for me its not about saving money. ShipStations support is where they shine. I've never had an outage for more than an hour or so and have never had to wait more than 10-15 minutes to talk to support, even on weekends or off hours.