Write SQL query to solve given problem: What is the category of the business with medium review length and highest review stars within business ID from 6 t0 9?. Keep the solution inside sql tag ```sql [SQL-Query] ```
SELECT T4.category_name FROM Reviews AS T1 INNER JOIN Business AS T2 ON T1.business_id = T2.business_id INNER JOIN Business_Categories AS T3 ON T2.business_id = T3.business_id INNER JOIN Categories AS T4 ON T3.category_id = T4.category_id WHERE T1.review_length LIKE 'Medium' AND T2.business_id BETWEEN 6 AND 9 ORDER BY T1.review_stars DESC LIMIT 1