Your questions were:

What is the difference between them? Why is one good and the other bad?

The differences between self-voting, mining and cloud mining are self-evident. To explain the differences here is akin to describing the differences between cats and dogs. A differentiation of their genetics while definitive, is unnecessary here because "differences" can be perceived on a much simpler level.

Perhaps, clarification is in order. What is the "bad" and what is the "good"? I assume you are talking about self-voting as "bad" in light of the recent HF-19 developments. However there are "bad" aspects to all three entities you are asking us to compare.

As to why "self-voting" is bad, I reiterate that whether something is good or bad depends on the context. There are no absolute measurements. While I don't perceive self-voting as "bad" under current Steemit regulations, there are those who do consider self-voting to be "bad" because the original intent of upvoting was for signaling and rewarding "good" content, not a push-button way to make money by self-voting IMHO. However, voting of any kind lacks merit for evaluating content on Steemit because of the reasons detailed in my previous comment.

Asking whether one is "good" and the other "bad" is a meaningless question because voting on Steemit is a failure from the standpoint of a method of evaluation of the quality of content, regardless of the reason. However, it does serve as a means of distributing the reward pool democratically.