What does it take to be a shipper of choice?
Or maybe the question should be: What does it take to be a Shipper of Choice?
The lowercase first version describes generally a customer that carriers consider it a pleasure to do business with.
The capitalized second use refers to a shipper that has earned a distinction from an outside observer, like FreightWaves, or possibly from a carrier publicly or internally bestowing the honor on a shipper that has earned it by reaching certain metrics.
On a SONAR...
https://www.freightwaves.com/news/sonar-webinar-chasing-the-coveted-title-of-shipper-of-choice