What the title says, what Horde race is the most savage/brutal in your opinion?
Personally I think it's a tie between Darkspear trolls and the Forsaken. The former being culturally savage/extremely brutal and the latter being more situationally savage/brutal. I'm more referring to the culture of the New Horde, so anything from the Pre-Thrall Horde doesn't really count.
Culturally speaking the orcs of the modern Horde are pretty liberal and mostly strictly persecute unfavorable traditions from Draenor. Durotar is also a lot more pluralist, enough so that there aren't a number of orcs leaving in droves because of the culture. Trolls on the other hand maintain such a brutal and barbaric culture that many trolls can't take it and end up living in Orgrimmar or Thunder Bluff. They also formerly practiced cannibalism and non-battle related sacrifices, both of which were frowned upon by Thrall and the orcs.