If you've already got staves I would use one of those for sure. I'm partway through my first couple of bows, waiting on string material arriving this week, and, while I haven't tried a board, the amount you'll learn working a stave with dips, knots, cracks, bends, holes etc. is immense and I personally think it's the best way to go.
Black Walnut is OK, but from what I hear you sort of want to have some idea of how to handle it before you attempt one of those.
Hickory sounds good I would go with that. Assuming the staves are "decent". If you could get some pictures up, people will have a much easier time letting you know if they're worth using or not. You need to show how straight the grain is and where knots etc. are positioned if possible.
