Popular with who?
So you want to know the Justin Bieber of motorcycles?
If you are going by the dictionary definition of popular then it would have to be the Honda Cub or in India the Enfield Bullet.
Not sure if you mean Thailand or worldwide. But worldwide, in 2014, the 87th millionth Honda Super Cub was built, making it the most produced motor vehicle in history.
If it's only Thailand, the most popular motorcycle ever would probably be the Honda Dream ...
Hello, what is the most popular motorcycle ever?