Final answer:
The most clearly written and grammatically correct sentence is: People who have hobbies are happier than others.
Step-by-step explanation:
The most clearly written and grammatically correct sentence is: People who have hobbies are happier than others. This sentence is clear, concise, and uses the correct verb tense. It states the subject (people who have hobbies) and the corresponding verb (are happier) in a grammatically correct manner.