Here's just a rundown of my likes and dislikes for the various demons.

Mors-gravis - Like blunt attack, don't like that its bashes almost always missed and mental knife alone seemed somewhat weak compared to other demons.

Harmentia - Didn't like that it did fireball all the time. It was otherwise pretty good. Somewhat liked that it was very aggressive and didn't attack you when you got low in health. Didn't land enough hits on warrior types, they seemed to tank it too well for my tastes. Its bashes always missed too.

Morosa - With the changes I'd use this more. Gore never really seemed to lag unfortunately. I'd have to play with this more now because before with the chained lightning I literally almost never used it so this one I don't know a ton about.

Challegha - Should remove or lower its auto-attacking ability even more mostly to a lower health (15% or lower). As an evil conjurer, you have enough to worry about. This was my favorite demon except I was almost never able to safely use it. The problem for me was that even though you could choose 4 demons, I always picked harmentia or mors-gravis because the other ones gave me too many mob deaths or would attack me while my enemies were attacking me and kill me off. Harmentia has some other restrictions so basically I wound up using mors-gravis a lot which, compared to the other demons, is sort of crappy. I can understand having limited selection, but compared to an angel mors-gravis just doesn't cut it.

Devils - Make them barrier more, I don't think that'd be unfair considering they're relatively bad in PK compared to demons. They don't enter into melee meaning you're tanking and they don't heal you. Barrier doesn't seem overpowered in light of that. Demons at least will tank for you so if you use a hit and run and hide-behind-the-demon they just always and unequivocably seemed like a much, much better choice than devils. Problem with evil conjies compared to good is the requirement (not suggestion) of using barrier. You tank like crap and you can't afford to lose health due to how servitors pounce on you. So basically you're left with the option of using demons to at least keep foes off of you and on them. That's how I played an evil conjie and it was successful but I just felt like 3/4 of the class left me open to too many ways of getting screwed.