Out of all cryptocurrencies that exist today, Bitcoin is probably the worst one for buying drugs online. It's pseudo-anonymous at best (compared to Zcash that is actually anonymous), slower than many others and if government agencies have tracking tools in the cryptocurrency space, Bitcoin is probably the most popular target for those tools.
Zcash is not anonymous; cloaked transactions are optional and hardly anyone uses them (so they stick out like a sore thumb). It also requires trust that the founders aren't printing hidden coins (due to its flawed "trusted initialization" procedure used at the coins inception).
Monero/XMR is the only 100% private, fungible cryptocurrency. All transactions enforced private by default, with no option to send an un-private transaction.
Out of all cryptocurrencies that exist today, Bitcoin is probably the worst one for buying drugs online. It's pseudo-anonymous at best (compared to Zcash that is actually anonymous), slower than many others and if government agencies have tracking tools in the cryptocurrency space, Bitcoin is probably the most popular target for those tools.