Trading, join a campaign or bounty and mining are the best one, gambling is not good to earn money because it's very risky to do and also you have a high chance to lose your money/coins too. If you have so much money, i think trading and mining are good to spend your money into it. You can get a nice profit by doing that two.
Based on my experience, trading and gambling is close enough because you can lose money too. I still prefer earn money by campaign, like sign campaign, bounty etc.
I don't say that trading is gambling but better learn a lot of trading technique or you just spend your money to "gambling-on-trading"