The fact that monero is not popular does not necessarily relate to money laundering but rather to the response of regulators and exchanges to high levels of privacy. Any crypto is liable to abuse, as is cash, and thus it is more of a perception than a reality that XMR is being targeted. Coins such as ZEC are privacy-oriented, however, they became more acceptable since their privacy is not mandatory, something that makes regulators feel better. The default privacy is the advantage of Monero, and it restricts the listing, liquidity, and mainstream adoption. Ultimately, its lack of popularity is motivated not by the purpose of its use but by the external pressure.
I believe ZEC's upsurge in price has been driven by hype. The coin was long lost and forgotten for a while, only to gain attention from investors recently (after a few influential people talked about it). The decentralized swaps feature, also had a positive impact over its price. As for ZEC not having "mandatory privacy", I think that has changed after shielded transactions were made the norm in one of the recent network upgrades. For what I know, ZEC no longer supports "t" addresses. Currently, ZEC sits at the #12 spot in market cap. Meanwhile, Monero is being left behind in the dust as exchanges continue to de-list it.
Between XMR and ZEC, the former is much more decentralized and censorship-resistant. I'd prefer Monero than Zcash for this simple fact alone. However, ZEC does have the same limited supply as BTC (and deflationary model), making it an attractive investment for anyone who wants to make money in the long-term. To my understanding, XMR is inflationary by design. Each coin has its own pros and cons. While a privacy coin such as ZEC had a good run, I wouldn't expect the craze to last forever. Not as long as governments continue to oppose anything that's privacy-oriented. Monero being unpopular is the least thing to worry about. As long as the network is alive and running, nothing else matters.