It depends on how you define "better". As a sibling comment points out: let's say that the AI is programmed to maximize the number of paperclips in the universe

It depends on how you define "better". As a sibling comment points out: let's say that the AI is programmed to maximize the number of paperclips in the universe. And then to accomplish that goal, it kills all humans (by eating our infrastructure to turn it into paperclips). But that's not enough. The earth's mantle and core contain massive amounts of iron and aluminum that could be used to make paperclips. So the AI starts consuming the Earth. And then it scans the rest of the solar system... ah, Mars and the asteroid belt contain lots of iron and aluminum too! I fail to see how a solar system turned into a ring of paperclips orbiting a sun is in any way "better" than what we have right now.