Let's say the local meta is heavy into 2 ship Imp builds, with 1-2 being VSD's set up as carriers. Fighters are a mix of stuff, but lots of Interceptors, Howlrunner, and often Vader. I don't know the meta of objectives for this.

I'm an Imp player exclusively, so far, and trying to counter with more of the same hasn't been too successful for me. I've also tried a 2 VSD + 1 GSD list with a handful of TIE fighters and that didn't work too well either. I now have a bunch of Rebel stuff, so I can work with either faction.

What would you do to counter this, as either Imp or Rebel scum?

At 300? One VSD and two GSD, a few ties for cover.

I'd use Neb-B Escort spam, with a few fighters to act as bait. If your opponents are using lots of interceptors, they ought to go down fairly easily to AA fire. Stay away from the VSD's initially (lateral movement), tempt the fighters in, wipe them out, then focus on the VSD's. Salvation helps a lot. Maybe redemption too...

That's the theory, anyways. It's tricky to pull off, but very satisfying when it works.

Quad gladiator-II’s with screed and a few concussion missiles should do pretty well. The AA fire should get you a decent few points against the squishy fighters (or force them to clear off and stop shooting you), and gladiators seem to do pretty well against victories in general.

Or just take GSD-I's and more concussion missiles!

Going first helps