Of the clients whose businesses are located in the city of Boston, calculate which of them has a higher average amount of payment.
average amount payment = AVG(amount);
SELECT T1.customerNumber FROM customers AS T1 INNER JOIN payments AS T2 ON T1.customerNumber = T2.customerNumber WHERE T1.city = 'Boston' GROUP BY T1.customerNumber ORDER BY SUM(T2.amount) / COUNT(T2.paymentDate) DESC LIMIT 1