As a first mover, bitcoin has network effects on its side. It has far and above the highest hashrate, or level of computing power devoted to securing the network, among those cryptos that use proof-of-work, a mechanism by which participants agree on which set of records is true. For this reason, bitcoin at the network level is (almost) impossible to hack (centralized exchanges are another story) and arguably the most secure coin in the most secure category. There are other consensus mechanisms, such as proof-of-stake, but none has been tested to the degree proof-of-work has.
