I’ve played a lot of both and here is my take:

-I would often rather omens blind then Astra’s pull and stun

-Omen gets multiple free smokes a round

-Omen gets a reposition ability

-Omen doesn’t have to go to different world to place abilities

-Omens abilities are less pre meditated

-Astra’s ult is much better

-Astra gets unlimited free 2 second smokes

-Astra has lower smoke cd