What mode of trade was the most beneficial to the city?

International trade.  Hope this helps!

Explanation:

Economic transactions that are made between countries. Among the items commonly traded are consumer goods, such as television sets and clothing; capital goods, such as machinery; and raw materials and food. Other transactions involve services, such as travel services and payments for foreign patents. International trade transactions are facilitated by international financial payments, in which the private banking system and the central banks of the trading nations play important roles.