Practice make perfect, the more you do something the better you get. Or in doing tasks you learn the short cuts of doing the task.

As for why you did not enjoy the manga style is that it is not free form, its very structured and static, with free form its more fluid and able to be well...silly, happy and child like. Another reason is that you started out with the free form style and its hard to take up another style once your so ingrained with it, though it would not hurt to see the way the other styles work to see if you can take something from it.