In flying to any place in Asia you want an airline that will take you there and has a reputation for having good decent service. The most frequently used of all carriers that fly to many Asian countries are United Airlines and American Airlines. Both airlines fly non-stop, but usually they have a layover in London, Paris, Berlin, Rome, and Athens or other cities in Europe, but usually they do non-stop flights. The average person will spend about 12-15 hours on a single non-stop flight depending on where they're flying. Most of the time you would have to change flights in either New York since some people fly to Asia that way or out of Los Angeles or San Francisco-though the flight is much longer going from New York to Tokyo with maybe a layover in Rome or Athens. Many foreign-based airlines have terminals inside American airports in certain cities that have the highest concentration of international flights and travelers who travel to Asia for business to leisure vacations. Some of the airlines have frequent flights to countries that have a lot of customers flying to them.
In recent years with the increase of traffic to places like Tokyo, Beijing, and other cities in Asia the airlines have been increasing the number of flights they put out per day to meet the demand of the market and the traffic that uses specific routes throughout the region. Some airlines did cut their routes short to Asia when they weren't drumming up enough customers. What's nice is that usually the international terminals for U.S. based carriers are less crowded than those who are on domestic flights since you go through a more thorough security check and through customs screening before being allowed to enter the terminal. Usually most international flights leave out twice a day in the morning and afternoon, but depending on the carrier if they have red eye flights-very late night flights, but usually red eye flights leave between 10 and midnight and land at their destination the next day or early afternoon. These flights can a lot longer than ones that leave early in the day. These are also the less crowded flights since more people will likely travel during the day instead of at night.
Night flights are comfortable because it's quiet and you can actually relax and sleep through the flight and some late night flights will show movies and serve a really nice dinner versus the snacks you're served in coach and business class. Some carriers will serve a nice meal depending on your flight and where you're going on your itinerary. Usually the flights to Asia going east from New York or west from California are the ones you can watch movies on and relax into a different time zone before landing so it makes dealing with jet lag a lot easier and less stressful on you when you officially wake up for the day since many travelers mainly those who fly to Asia will deal with a higher level of jet lag since the flights are a lot longer.