Buttons should flow sequentially in the reading direction.

That means in English reading direction is left to right. So, buttons would be 1 - 2 - 3 upwards on the left, then 4 - 5 - 6 downward on the right. (Basically the reverse of your screenshot)

This keeps the eye moving in the same direction when reading the elements. You don't want users to read, then have to backtrack in order to find the next element. You want a nice, smooth, flow for the eye.

Elements should flow sequentially in the reading direction.

That means in English reading direction is left to right. So, buttons would be 1 - 2 - 3 upwards on the left, then 4 - 5 - 6 downward on the right. Basically the reverse of your screenshot. - (edit) However, it does depend on the text baseline and reading intent. If, as you have it, the text has its baseline facing outward, then you have things correct in the screenshot.

_{I didn't notice the baseline until I viewed the screenshot larger.}

The goal should be to keep the eye moving in the same direction when reading the elements. You don't want users to read, then have to backtrack in order to find the next element. You want a nice, smooth, flow for the eye.