Don't forget unless you mod it, RoR units don't benefit from your tech or lord bonuses so you can very easily end up with regular troops being stronger than them. So I would say I would grab quarrelers or standard rangers before I grabbed Bugman's. That being said, I would totally get the axe throwing rangers before either of those. Those things are so scary.
I kinda treat most RoR units as just emergency troops anyway. There are only a few that are actually fearsome.
Like, for the Dwarfs, the only ones I actually take note of are the steam Irondrakes, the RoR Hammerers, and the super Gyrobomber. The rest are just... meh.
They're good for MP since they're cost effective there, but in campaign you usually end up with stronger regular infantry.
Okay, I've been checking this, and it is not, I repeat not true.
My Norgrimling's Ironbreakers and my normal Ironbreakers have the same armor boost from the armor-up, and I am only running the Trait Description mod for the purposes of "How'd THAT happen?"(On a related note, executing prisoners gets you bad traits.

).
In addition, the Dragonback Slayers have 5 Armor from the Dorf infantry tech, despite being, well, Slayers.
So tech does, in fact, boost unique units.
Now that's done, a question: How play Chaos on the field? I'm thinking lots and lots of Chosen, basically just them, some Dragon Ogres for linebreaking, and a pair of Hellcannons as arty.