During Rogue One, we see that Krennic is largely responsible for getting the first Death Star up and running, and that the test they do an the desert planet is completely successful beyond what anyone expected.
Grand Mof Tarkin sees this as an opportunity to make himself look better to Vader and the emperor and decides that he'll take control of the new weapon. That makes sense, as he's looking out for number 1.
Vader also seems to really dislike Krennic, though, and I don't understand why. He sees that Krennic has aspirations for grander things. But the thing is, Krennic gets stuff done. He actually went out and got the resources to build the thing and then built it! It seems that Vader should want to promote him to get more stuff done.
Why does Vader dislike Krennic so much?