Companies
Despite what you might have heard, all airline carriers are not created equal. How good or bad an airline is fully depends on the company's rules and policies, which have drastically changed over the years.
Additionally, whether an airline is domestic or international makes a difference in the standard of service and comfort. Most international flights have at least decent service because of the length of time flyers must spend on the plane; it is often better even than domestic flights.
United Airlines, Continental, Delta, American Airlines and many more have all gone through major transformations in the last decade, some of them good, some of them not. Some great advances have come in the form of personal TV's, games, interactive activities, healthier food and more comfortable seating.