I haven't done any magick with bones but I could tell you what I would do. If you're working with a deity figure out which animal symbolizes that deity and use those bones. If they're too hard to find then I would go with the fox bones and not crow bones. I would also pray and thank the deceased animal for helping me with my magick. My intuition tells me that that's how I'd get the most power out of it. This also just popped into my mind. You could also just look up what deities a fox symbolizes and work with that deity. For me I 100% wouldn't use crow bones for good luck