I love
Annabel and don't find it sickly-sweet at all; it sounds energetic and echoes right down Scottish history. And I also love the bizarre etymology!
Which is one reason why I so dislike
Annabelle. In becoming fake-French it loses its meaning.
I once knew an
Annabel Suzanne! I found that bit much. But as a sibling for
Annabel,
Susannah would be practically guaranteed to be known as
Susie rather than
Annie, which is good.