Trade is the best bitcoin revenue today. Some people invest in HYIPs, however, that is wrong, they are choosing to go into the path of the scammers.
That might be true, but only in case when the person is a talented trader, with required knowledge and education.
Getting into HYIP's is also nothing really profitable, in the most of times when you are depositing your funds on the address of some HYIP you are not going to get your money back, not even talking about the profits that the "company" has promised to you.
There is only way when you can earn on such a scam: you need to enter it as soon as possible, and you need as many referrals as it is possible: with that, you can get really decent money from such an activity.
But do you really want to lie to people because you know that they are going to lose their money?