Honestly, I like the demon girls here so much I'd recommend doing the genocide route first, and then wiping the data as in method 4 from my post before and then doing a pacifist run. Since, I had a hard time doing a genocide run after doing a pacifist run. If you just want to enjoy cuteness and cuddliness I'd say do a pacifist run and then do a newgame+ with the pacifist run bonuses.Say, this is my first play, and I'm at a fence to juggle between pacifist or genocide. So which one should I do first? Also if I do go to pacifist route do I not get to kill anyone and just maintain lvl 1 throughout the game?
That being said, there are two special endings that can only be obtained by doing a pacifist run and then doing a genocide run so if you want to see those endings you will need to do a pacifist run 1st. (After you beat the game there is a method to start a new game without newgame+ stuff)
If you do go the route of doing a pacifist run you will have to stay at lvl 1 the entire game (don't worry seeing scenes and befriending the demon girls does give you SP just like if you were leveling up), use no assistance from Hell (the ghost and his secretary), no killing, and there are a few times where you have to use chapter select to go back and redo a section with new information that you got from later on in the game. Example: There's a boss you kill that afterwards you find out the truth and have to go back and re-confront her and fight the real boss instead. There should be a walkthrough somewhere through this thread that tells you how to do a pacifist run if you want a walkthrough.