The most dangerous race is: tormentors/taken or scorn. They are paracasuals creatures. Tormentors are the most dangerous opponents. And the only weakness they have is low population(I think). Taken are pure darkness that can "take" enemies. Scorn basically are immortal. But they need to have a leader, cause they mindless. Vex easily defeated so many times with all their technologies, cause they lack paracasuals powers. And could easily be corrupted by taken, hive, fallen and even humans(remember Asher Mir) Other races nowadays feels pathetic. Just like humans but weaker.