There appear to be 5 candidates revealed: Sawyer, Jack, Hurley, Sayid, Jin or Sun and another (Ilana has said there are 6 left). Though, Ilana and MIB aren't sure if it's one or the other Kwon or both. If it's both, then we have 6 already.
Is the title referring to the one that is ultimately chosen to replace Jacob? That would be interesting if we were to find that out.
MIB wants these 6 to get off the island with him so he can leave. He apparently wants them to stay alive. Kate's not a candidate, but he'll use her to get people off the island, then he appears not to care if Claire kills her.
I don't know what Jacob wants, really.
MIB understood that if Jacob died, he (MIB) could leave. Jacob said someone would replace him so that MIB couldn't leave, but Jacob's been dead... is there a grace period or something in these mysterious Rules? I guess that (loophole?) could be why MIB wants to get the candidates out now and things have been put into motion at the temple and with mention of an escape plan, but I would think if THE candidate wasn't ready to take over right at Jacob's death that MIB would be free to leave. That's how it would work in the real world I guess. But I guess one would need to be able to predict one's own death for that to happen. Jacob can grant eternal life, though, so is it really a stretch to say he would be able to predict his death? Jacob thought Ben wouldn't kill him, though, so maybe he died before he finished the selection process- if he's the one picking. Do we even know that? Not that Jacob's being alive or not seems to matter since he can talk to Hurley...
On the Official LOST Podcast (May 7) Damon and Carlto made a few relevant points.
They wanted to take out half the candidates in one fell swoop and to show that Locke was bad.
They wanted to leave no doubt that he is a force of antagonism. They wanted to show Locke finally putting his plan into action to get all the candidates together to kill them.
I would say that he definitely has opposite goals to some, but is he evil? I don't know.