I have not examined exactly what zcash is doing, but zero-knowledge-proofs (ZKPs) can probably lead to cryptocurrencies that are even more anonymous than Monero or (hypothetically) mimblewimble. However, zk-SNARK ZKP systems have the trusted setup weak point. ZKP-based altcoins should take extreme care to do an especially secure key ceremony. They should have a many-page report explaining exactly how everyone can be 100% sure that the key ceremony for the trusted setup was done securely. I don't invest in altcoins anyway, but if I did, I would never even consider investing in a ZKP-based altcoin without convincing info about why I should trust its trusted setup.
It's also important to realize that the zk-SNARK crypto is new and immature. I wouldn't be all that surprised if someone finds a way of totally breaking its security someday. The code itself may also be weak -- a year or two ago a flaw in the most popular zk-SNARK library was found which rendered things relying on it completely insecure, for example.