I haven't explore that much in bitcoin, but I have tried mining and currently on a campaign. I have little ideas about trading and gambling, but for me, I would prefer trading and campaign. In mining, you need a high end computer in order to mine coins, you also need a fast internet connection and probably a source of electricity that will not cost you a lot of money. Gambling as we all know is hard to compete with. People involve in it are high rollers, and some are war freaks. Meaning, if you get to bump to them, expect that death is at the tail of your trail. That is why I prefer trading and campaign. Although its a long process before earning, still its safe. Just no to scammers.