top to bottom.
I practiced this test until i was blue in the face and found i was much faster top to bottom. i struggled to finish going left to right sometimes.
And because of this practice, i specifically asked if i had to go left to right like on the dots to which she said no, do it how you like.
Honestly, i don't think this is a test you can afford not to finish or get in the mindset that it doesn't matter not to finish, i know some don't finish and still pass however best to make sure. However, with some practice it isn't that hard to whizz through it.