I am wanting to start knitting in circular needles for hats

, this will be my first time. I am really sick and tired of the knitter looms, they don't come out how I want them. And it seems that using circular needs will look more neat, from what I have seen
I have found that they come with 16", 24", 29", and 29", the cable area. If that makes sense.
I want to make hats for kids and adults. I know I want to do them on a 8 USA needles. But which circular needles do I need for these kind of hats? The 16" and the 24" or all of them?