From personal experience and working in the travel industry for 10 years, the few times when I ran into issues and needed to get someone to help, the best customer services were always provided directly by the airline, and almost never through any Online Travel Agencies (OTAs) like Hotels, Expedia, Booking or Priceline.

Booking with OTAs almost invariably end up with the flight operator (airline) and the OTAs pointing fingers at each other when something goes wrong. Therefore, if you’re looking only to purchase standalone airfare, I highly recommend booking directly through the airlines’ websites.