This was the first quest that I acquired that was difficult to make a decision, as there isn't a true "good" or "evil" choice as you would find in the older D&D universe. My first character sided with Raedric and went & killed Kolsic, returned and let Radric remain on the throne, justifying that this region needed stability. But that bothered me that whole play through because of Raedric's cruelty to the people in his kingdom.
So on my 2nd character (started new game with the White March dlc), I really wanted to destroy this bastard. Once I got to the throne room, I know for a fact that I will die if I attack, I was out numbered more that 2-1. I'm a level 4 ranger with only 3 companions (at this time): Eder, Aloth, and Durrance, plus my animal companion. I conversed with Raedric and agreed to "investigate" Kolsic, as opposed to "killing" Kolsic. Which seems reasonable, since I have a chance to hear both sides of the story.
Approaching Kolsic in his hideout, I was again out numbered more that 2-1, and insta-death was certain if I attacked (it was, I tried it) at level 4 with only 3 companions. (A side note on this: I think this encounter has increased in difficulty since the 2.0/2.1 update, as I don't remember this encounter being that difficult with my first character. But I like the increased difficulty as it makes me think more about tactics before I attack, or if I should attack).
So anyway, I reloaded a save before Kolsic's hideout and decided to move on to Caed Nua. My reasoning is to have a stronger party, then go back and make that decision whether to side with Kolsic or Raedric. I'm still, at this point, leaning towards Kolsic, because I don't like what Raedric's done to his town. Also, there is a member of Kolsic's party(can't remember his name) that I freed from Raedric's dungeons, and I don't really want to kill him after I had saved him from torture.
Story-wise, I think it is logical to talk to both Raedric and Kolsic, and then decide who you'll side with.