So, according to your poll, either have difficulty be set to the way the user wants it, or be forced to one of three settings.
.... Yeah, I can't see a single benefit to your "Easy, Normal, Hard" Those would be more ore less equivocal to 3 points on the slider, without any options. Gotta go with the one that gives me more options.
This.
The difficulty slider is one of those many things I wonder why people want to be rid of, because it
subtracts absolutely nothing from the game. Yes, it would be nice if the "difficulty" was something more than just increasing or decreasing enemy stats, but removing the slider altogether isn't exactly a solution to that.