i think you can use both directional fabrics but save them for the blocks that its easy to control the direction.
dealing with directional and paper piecing just adds one more element to the challenge.
save this fabric for when we get to applique or when we hit the christmas holiday season.
it will be easier to control the direction on those types of blocks.
you won't have to worry about cutting in angles in the opposite direction so that the directional print goes the right way when paper piecing.
i did this on one block and i won't ever do it again - it turned a 1 hour block into 3 hours of work.