I've had a good experience with war dogs, and usually release them when the battle has tilted in my favour and there are some enemies out of reach, like archers. They die easily, however, so you need to time their release well. I've sacrificed some during pitch battles, to save my mercs' some hits, and I regrettably lost my last pair due to a poorly-timed (early) use against a band of orcs.
I figure they would also be useful against Goblin Ambushers, too, but I haven't faced that variety of greenskins yet.
As for unique warbeasts, I figure a rare tamed direwolf would be cool, but it'd likely be uncarriable due to its size, and largely uncontrollable (therefore easy to lose) unless specific mechanics were designed to rein it in. Something like specific handler commands. The way I see it, a Houndmaster background would be a must to have access to them.
Day 57 - You have seperate sergeant and bannerman? I figure if someone has high enough resolve to carry the banner, they're usually the ones to get rally as well.
I suppose I didn't plan it well initially. The first Sergeant had a two-handed axe and I think was specialized in it, so I couldn't move him to the back line without giving up that advantage.
When the first Sergeant died, the brother with the highest resolve was a first line specialized spearman, and again I couldn't relegate him to the rear. The bannerman is the same guy with unexceptional Resolve who took up the standard when the company first got it, now level 6 and specialized in polearms, obviously. I try to increase his Resolve whenever I can, but it isn't his forte, either.
EDIT: New update out!