Debating on last name

Ok In need of opinions and thoughts ladies.  I've recently been debating on whether I should give my baby my last name or her father's last name. I've been debating this because we have been falling apart, although I'm hoping for a future with him, it's been rocky. He already has a daughter with his last name so I wouldn't see the harm in having the child we share together my last name.  Thoughts??