the biggest diff between bitcoin and zcash imo is not privacy or quantum resistance, but the fact that the latter is capable of changes and the former is not.
and this is a tradeoff rather than strict superiority. ossification of bitcoin does offer stronger guarantee of immutability and fixed supply, whereas zcash can better adapt to the latest threats (eg quantum) and user needs (eg growing privacy concerns).
this is why if believe in the value of non-sovereign money u probably want to hold both (at a ratio that reflects their relatively level of maturity and risk).