Which of these are grammatically correct?

authors choose a genre based on their purpose. fiction works well for teaching a lesson, as in fables. however, presenting facts and opinions in nonfiction might be a better way to present information. when authors begin to write, they think about what they want the reader to understand or experience. while fiction may be the best genre for storytelling, nonfiction may be the most clear for sharing facts, so both genres have merits.