Both forms are correct. There is, however, a guideline (not a strict rule!):i've noticed that with some irregular verbs two variants are possible,
like jij kan or kunt, u zal or zult.. how do i know which one to use? Are there any rules that can give me a clue?
In the Netherlands, the 'a-form' (kan, zal) is more informal, colloquial.
The u-form (kunt, zult) is more formal and preferred in written form.
Note that the Flemish do not consider the a-form less
formal than the u-form.