I'mma say SFK. Though H BRC is relatively idiot proof, there are seemingly a lot of tanks who just don't get it on karsh as well as the idiots who group kick you for suggesting don't let the stacks drop at all. Obviously letting the stacks get to 15 is the heroic achievement, so whether or not continuous stacking is the intended way of doing it, I can't be sure. Once you can get that through your tank's skull, it's pretty facerollable. Still. SFK. Optional boss is a bit of a trick but the trash is easy mode.