Bitcoin is secure for most purposes, but since all transactions are recorded on a public ledger, they can potentially be traced. Monero focuses on privacy, concealing the details of a transaction-the sender, receiver, and amount. This makes Monero very popular for anyone seeking to conduct private transactions, however with this level of privacy and anonimity you will also raised a suspicion that people who use monero might use it for something illegal. On the other hand bitcoin is also working on its privacy with updates and second-layer solutions. In the end, it depends on your priorities: if you are mostly worried about privacy, Monero might be a better fit; if you would prefer a widely accepted and open one, then Bitcoin is still a good option.