idea
Dictionary and HashTable are both implementation of IDictionary.
Dictionary maintains order, so values are iterable in $O(n)$. Provides better performance than HashTable on value types[2].
HashTable are weakly typed. Should not be used, instead use Dictionary[3]. Return null on key doesn't exist. Requires boxing, i.e. casting to and from object, which is computationaly expensive for value types (20x factor rather than reference assignment[1]) that need conversion to objects.