a) BTC-BTC Transfer: Only BTC transfer fee. Beats TransferWise by a large Margin.
b) BTC-USD: Depends on many variables, including if the receiving country taxes BTC to fiat. Considering how expensive transferwise is, it's probably a wash.
Speed depends on if GP literally meant Cash. If so, BTC is obviously far faster and easier as you still need to get you cash into your bank account. Otherwise… Transferwise takes a few hours, BTC 10-20 minutes I think?
Privacy: The Banks and TW know who sent how much to whom. With BTC everyone knows that A sent X to B, but not necessarily who A and B are. As this transaction is public forever, I'd probably prefer TW from a privacy perspective, this of course changes with something like Monero.