From an employee perspective, comparing Delta and United airport customer service has Delta far ahead in terms of corporate culture and job satisfaction imo. I think the same for flight attendants considering Delta’s able to stave off unionization—they’d have to be keeping flight attendants happy to do that.

Having fewer irops means less frustration and happier customers and employees, so that probably factors into employee pleasantness. Flexibility to resolve customer service failures helps, too. It’s frustrating to want to help someone, but not have the tools or power to do anything. I think Delta is better than other airlines at keeping employees happy by keeping ops running relatively smoothly and empowering employees to resolve issues. Happy customers and happy employees influence each other.