I voted Gabriel. Being Christian and having lived in the South, I've met more than one Nehemiah, but it just seems like a hard name to live with. There are no intuitive NNs and it's apparently hard to pronounce (I've always known how to pronounce it, but, you know...church). Isaiah is a nice name and I like the prophet, but I just generally like the sound and feel of Gabriel better.
Re: Which is better?
Make a pregnancy ticker
N-name.
Back when I was still teaching, I had a student named Nehemiah, and I really liked it.