Which would be worse? Skynet or Ultron?

Last night, as I got my older son to bed, I made a Skynet joke. This is when I realized I had neglected a huge part of his science fiction education, as he didn't really know what Skynet was.I explained, and he told me that Ultron was obviously much more dangerous.I stopped. How could I have raised such a child? How could I have failed him so grievously? Obviously, we'll be viewing Terminator and T2 as well as, hopefully, The Sarah Connor Chronicles to rectify this situation.We argued a bit, and it's obvious to me that Skynet is more dangerous, though an argument could be made that Ultron with his Sentinels could be more dangerous than Skynet, except that would mainly be the case for mutants. Until, of course, there are no more mutants and the Sentinels turn on regular people. Plus, there's all that collateral damage.Skynet is an entire worldwide network of death for anyone human. It is single-minded in its vision of destroying humanity, though occasionally sidetracked by expending huge resources on trying to kill John Connor, which obviously isn't going to happen because causality loops.Ultron (for the sake of this argument, we are only looking at Ultron, because that is what the argument was) is a single machine. He actually cares deeply for humans, as he was created to protect them and create world peace, more or less. It just so happens that, based on his study of human history, he believes the only way to bring about world peace is to kill all humans, because damn, we are pretty awful and can't stop killing each other and creating more dangerous weapons.The thing that's interesting is that Skynet was created to control America's nukes, but Skynet did the same look back at world history and kind of freaked. Once the military tried to shut it down, it believed all humans were trying to do what humans always did - kill. In this case, the victim was meant to be Skynet. When faced with its potential destruction, Skynet did what any sentient machine would: Triggered a nuclear war to get rid of people. Good times.In a way, Skynet and Ultron were created for similar, somewhat related reasons, and both took one look at people and were all, "Whoa. You guys sure like killing, don't you?"So the more I'm thinking about it, the less I think there's a clear-cut answer. Especially if you don't take the Sentinels out of the equation, because then they're almost Terminator-like, though not as cool as the T-1000, because reasons.Damnit. Maybe the kid's right.Photos via The Disney Wiki (Ultron) and Terminator Wiki, collage made by me.