One more thing that sets Bitcoin apart is the immense decentralization - in hashpower, full nodes, development and community.
For security, the first two are the most critical.

Most altcoins either don't have node synchronization or / and they have a flawed consensus mechanism (proof of stake) that simply gives the developers total power over the project. This allows them to change rules at will, but also allows authorities to press them to do such things. In Bitcoin, that's simply impossible.
A PoW coin with not enough hashpower can be attacked similarly, and as a matter of fact most energy is pumped into Bitcoin PoW, which makes it most secure.