The fastest way to make gold will always be buying gems and converting to gold with real money.
Realistically you can break it down like a job. How much would you pay yourself to play per hour? How much gold do you want and many gems/real currency does it cost? Now figure out how many hours it would take to make that much gold.
I watched one of Lara's videos recently and legendary fishing is one of the fastest ways to make gold, but it's also rather boring.
Why is Gamora?