Every crypto-currency has it's zealots but that's not to detract from what Snowden said about Monero, labelling it "amateur crypto".

Ring signatures have been around longer than zk-snarks so time will tell on that comment.

I do however believe Zcash could be doing a better job for privacy, notably by mandating private transactions once the new "JUBJUB"optimizations have been merged [0].

[0] - https://z.cash/blog/cultivating-sapling-faster-zksnarks.html

Any idea how well alternatives like zcoin might hold up over time?

I don't know much about Zcoin. Looks promising if the description is to be believed.

Self-fulfilling prophesy right there.