The author acknowledges that Atomic Habits builds upon some of the content laid out in The Power of Habit, and so if you had to pick one of the two to read, this one is not it! The one benefit this book provides is that James Clear provides more practical advice on how to build your habits (which The Power of Habit doesn't do).
However Charles Duhigg does a better job of mixing science, facts and small stories about habits to prove his point - you can tell he's the better writer.