They are both pretty names, but I would definitely lean towards Aliyah as it is far less common. I'm sure you are already aware- but just incase you weren't- Aliyah is an old Hebrew name that means 'Rising;Ascending;Exhalted'- very nice meaning.
How would you pronouce it? 'A-lie-yah' or 'A-lee-ya'? I love them both but I would maybe lean towards the 2nd pronounciation as it may sound like you are saying 'A-liar'?
I'd hate to put a spanner in the works, but I just thought that was worth mentioning!!
Still love that name tho.....