Write SQL query to solve given problem: For users with average ratings of 3, what kind of tip length they mostly left?. Keep the solution inside sql tag ```sql [SQL-Query] ```
SELECT T2.tip_length FROM Users AS T1 INNER JOIN Tips AS T2 ON T1.user_id = T2.user_id WHERE T1.user_average_stars = 3 GROUP BY T2.tip_length ORDER BY COUNT(T2.tip_length) DESC LIMIT 1