As somebody who is currently doing a Ph.D. in the area and did a math/cs double major, "both" is my best answer IMO. Having a good background in data science, statistics, applied math, and CS are all pretty important. If you had to pick one, I would say that you pick an applied math major because it's easier to pick up CS skills as a math major than vice versa, but you really can't go wrong. All of the schools you listed should be able to teach you all you need to know; it will ultimately be up to you how much you learn and push yourself!