In Avengers: Age of Ultron, did Vision kill him or absorb him?
If he absorbed him, is Vision partly evil?
According to this wikia he did destroy Ultron
Vision: You're afraid.
Ultron: Of you?
Vision: Of death. You're the last one.
Ultron: You were supposed to be the last. Stark asked for a savior, and settled for a slave.
Vision: I suppose we're both disappointments. [Ultron chuckles]
Ultron: I suppose we are.
Vision: Humans are odd. They think order and chaos are somehow opposites, and try to control what won't be. But there is grace in their failings. I think you missed that.
Ultron: They're doomed.
Vision: Yes. But a thing isn't beautiful because it lasts. It's a privilege to be among them.
Ultron: You're unbearably naive.
Vision: Well, I was born yesterday. [as Ultron goes to attack him Vision uses the infinity stone in his head to destroy him]
before this, when Vision first awoke and Banner asks if the monster Ultron created him to be, Vision indicates that Ultron must be destroyed
What will you do? I don't want to kill Ultron. He's unique, and he's in pain. But that pain will roll over the earth, so he must be destroyed. Every form he's built, every trace of his presence on the net, we have to act now. And not one of us can do it without the others. Maybe I am a monster. I don't think I'd know if I were one. I'm not what you are, and not what you intended. So there may be no way to make you trust me. But we need to go.
This is also confirmed on the Marvel Cinematic Universe Wikia
Vision agreed, but claimed that something is not beautiful because it lasts, and that it was a privilege to be among them. Ultron sneered and described him as naive. After Vision wittily answered that he was born yesterday, an angered Ultron furiously lunged at him, only to be destroyed, thus permanently ending the threat he posed to the world.
Of course even if Vision did absorb Ultron, we don't know if he is or could become evil. At the very least we know one thing,
Tony Stark: Right, so, if I lift [Mjölnir], I...I then rule Asgard?
Thor: Yes, of course.
He gets to rule Asgard.
So Vision in the original story, not the movie is an evolution of Ultron which was by the way created by Hank Pym and not Tony Stark. So to answer your question whether he was evil. Well, Vision never attempted to destroy the world, but he did fall in love with Janet Van Dyne and had an affair with her to where she left Hank for Vision.
Of course that aspect of the story did not make it to the modern day movie versions of Marvel.
Hank has always been an insecure man which is why he went from Ant-Man to where he would be ridiculed by the other Avengers, then to Giant Man, because he thought this would help him deal with his insecurities to Yellowjacket, then creating Ultron and then Vision.
Just to add on the answers given above, this is in context to the movies and not the comic books, in Avengers: Infinity War (wiki here)
According to Tony Stark and Bruce Banner, Vision's personality is an amalgam of their own, Ultron's (excluding the megalomaniacal aspects) J.A.R.V.I.S.' and an unknown amount of variables derived from the Mind Stone. Vision is a polite, calm, and thoughtful being, in a similar manner to J.A.R.V.I.S., shown when he apologizes to the Avengers and the twins after just being brought to life. Unlike Ultron, he values all forms of life.
In Infinity War Shuri tries to remove the component of vision associated with the mind stone, as it is more than just the stone , or just Ultron or any other single personality for that matter. So even though Vision absorbed Ultron in order to destroy him , the amalgam of personalities made him a unique android and in no way evil.
Coming back to this during Wandavision - as Shuri stated. Ultron is a part of Vision. One of the many overlays that comprise him. I theorize that when Wanda ressurected Vision, she also ressurected Ultron's code and that the hex is a reference to him as it is referenced back in age of ultron. The reference to the Internet in the recent episode and the broadcast signal being picked up could be evidence of Ultron's code being scrambled up somewhere within the hex as everything thst enters the hex assumes a form befitting its use. He is also resurrected in the comics to battle the avengers when she totally loses her mind so this would be one potential way to reintroduce him.