The Ambassador. The conspiracy has to do with the autopsy report showing that he had to have been shot from no more than a few inches, whereas Sirhan was a couple feet in front of him. Also, the fatal shot appears to have been fired from behind him, or to the side. Sirhan confessed but says he has no recollection of the shooting. A bunch of people said evidence was confiscated.
Not that I'm hardcore on an RFK conspiracy, but it seems more likely than JFK. The official story on the JFK assasinaion pretty much makes sense on the surface, despite what some say.