Hi Angela,
Choosing a name is a very personal decision. Sometimes it helps to wait until you meet baby to see what name fits best. There is nothing worse than a name that doesn't 'fit' the person's personality.
In my opinion, though, from your list of three I would avoid Jennifer - soooooo many Jennifers out there. Mercedes - too much teasing from other kids with car references. That leaves Bianka - original, and doesn't rhyme with anything for teasing.
It's tough though, because you could have personal connections with the names. For example, my middle name is Margaret (fifth generation) so I felt obligated to use that name with my daughter even though I had no interest in doing so. We created, or came up with Marlee. Mar from Margaret, and Lee is my mom's middle name so she felt that her name was still carried on somehow.
Good luck with your decision. It is one of those things that when you hear the name, you will know - no doubts.
Happy Holidays,
L.