For anonymous transactions, many coins are suitable: Zcash, Monero, Dash, Verge, because they are all similar, but you need to look not only at anonymity, but also take into account the popularity of coins, liquidity, the number of exchanges on which they are being traded, and ease of use. For example, in the DarkNet from anonymous coins Monero is used more often, but for example, I like Zcash more.