I choose hive based on there actions compared against the others none are more gruesome sure the vex turn worlds into machines but the hive simply leave behind empty shells filed with there own abominations not only that but they live off of pain and suffering they infect planets with seeders and who the f*ck knows about onyx they literally rip guardians apart instead of just filing them with laser beams and not give 2 f*ck later they really enjoy killing guardians and make every moment last and just straight freaking ugly in general good job bungie for putting something unique and truly terrifying in my dreams at night xD there the only race to carry a f*cling knife(sword) to a gun fight(and against all odds) win the hive don't really have similar technology compared against the fallen etc. They instead worship a dark god (satin pretty much) and bend the rules of physics with the power said god provides they shoot screaming rockets Jesus and if that couldn't get any worse well my god they dramatically rise out of ink black liquids whenever they freaking like it pfft vex teleportation okay they say impressive please keep in mind hive have ships that also teleport when ever they want with screaming homing missiles yay some may call this over kill until you see thrall with shreak right behind it'll all be ogre now then you'll think its complete madness which is what Toland became once he tried to study them XD