I HATE BALVERINES. 

I liked fighting bands of mercenaries much better. Balverines are fast and strong and they do that thing where they leap straight up and land behind me so I'm swinging at thin air like some kind of fool.

I noticed that they didn't really show up in the game until after I'd made friends with the mercenaries by visiting their new tourist-trap camp. I still encounter bands of mercenaries from time to time, however, so the game hasn't replaced mercenaries with balverines entirely. 

So, there are two parts to this question:

* What is the most effective way to fight a band of balverines? Is there a particular combination of spells that scares them off? Or is it firearms or a sword that will make short work of them?
* Is there rhyme or reason to when I'm confronted by balverines and when I'm confronted by mercenaries? If, for example, balverines only show up at night, I will make a point of only traveling through those certain points where you get attacked by stuff during the day. I don't think it's that simple, however.