I fly several times a month with Delta, so my experience is an average of many flights in the US and overseas. They regularly provide friendly and flyer-focused service. Their flight attendants and gate agents have a smile and do what they can to make your trip the easiest it can be. There is no preventing bad weather delays, but with hundreds of flights, I can count non-weather delays of more than a few minutes on one hand.
Their recent fleet upgrades have added both continental and intercontinental wifi, large tv screens, and better seats. I love their flat bed pods in first class.