I owe my exposure to nightmare difficulty to Joram (the forum member

). I play on nightmare because it was suggested to me and I seem comfortable with it... and also because I have this rpg rule "never ever slide the difficulty down in a character's lifetime, only up."
I can't say the names of my characters since I use my real name for them in-game. I'll just name them generically, "Warrior" and "Ranger". Warrior finished DKS Ego Draconis on Normal, for experimental purposes he also finished the arena and dream fight on Hard. He finished FoV on nightmare all throughout.
Ranger on the other hand started and finished Ego Draconis on nightmare. He had a tough time on the arena being sort of interrupted and had to rely on his undead creature all throughout to divide the enemy's attention. He is now in FoV. He spent his time being a pure ranger (explosive arrows and magic missile) until he came across an epic two handed weapon in one of the flying fortresses. This character is quite lazy and instead of jumping around Ranger enjoys the most hiding behind his undead creature spamming explosive arrows (he also enjoyed explosive arrows in broken valley since he power leveled on the Orobas Fjords to get them early).
Currently, Ranger seems too powerful in FoV (still nightmare), more powerful than Warrior. So, he's no longer power playing but actually role playing and just enjoying the story.