[Kranar]

Technically is a very valid opinion if you're writing software that needs to be robust and secure in the face of user input. std::set is guaranteed to be logarithmic strictly in the number of comparisons in the worst case without exception.

std::unordered_set has some very difficult to reason about worst case scenarios that must factor in both the size of the collection and the hash function. Unless you are very careful about the type of hashing you use, you can easily be vulnerable to DDOS attacks that scale on the order of O(k * n) for key size k and container size n.