This question is something I have heard so many times that I stopped counting years ago. I believe the answer is that it depends on the writer.
If the first answer that comes to mind is characters then that is your default or your primary skill. If the first thing that comes to mind is plot and then characters, then plotting is your primary skill.
Either one works. The importance here is that usually your primary skill is your strongest one. Your secondary may need more work to get the best for your story.
Stories need both plot and characters. If one is weak and the other strong, the story isn’t balanced and often leaves the reader with questions and confusion.
Because my primary is characters, all my stories begin with the people. If I can’t feel as though I know them, if I can’t wonder what they will do next, I won’t be happy with the story they tell me. In short, if they are not real for me, they won’t be real for my readers
As for the plot, I hammer on it throughout the creative process. Since I know it is not my primary skill, I pay extra attention to every detail and research anything about which I have a question.
I want the reader to enjoy my books not wonder if I bothered to research the various aspects of the plot. I hope the readers enjoy my characters as much as I enjoyed the sharing of their lives.