Who is "more" biologically related to me, my full cousin or a half niece?

Would a cousin from my mothers side of the family, full blooded (my first cousin) or a "half" niece from my mother's first marriage, my half sister's daughter who isn't related to my father...Been pondering this for a while now and it's driving me insane :P Thanks in advance! I'm leaning towards the first cousin since genetically we have the same blood, right?