I voted for Ava. Marlee is ok, but Karlee is better. Not an option I know.
And as a school teacher, I thank you for choosing a short name that will be easy for the kid to spell. You don't know how many kids have very long and strange spelled name. Simple is better. Another plus, is that she wouldn't have a nickname.
Congrats again on the up-coming arrival of beautiful Ava or Marlee or a combination of them both.