Just wondering what you all have found as the most fun to play from the core rulebook?

I like doing competative terrain placment then use the battle builder for objectives.

I agree, we used the battlebuilder more than the scenarios.  The tournament battlebuilder is a little more fun.  We really had alot of fun with the 3 player scenarios from Zverograd book.  In particular the At All Costs scenario we call the meat grinder.

Secret Objective, hands down. Makes the game more interesting, and turns it into plotting and anxiety rather than a simple slug-fest. Try it.

I prefer the battle builder as well. I think it is actually one of the many great selling points for the game.

You can try to tailor lists to the strengths of some of the various battle builder scenarios.

The amazing thing with the Battle Builder is that the proper combination can equalize any two armies.

A little off-topic but do you think that the Battle Builder can be used with Dust Tactics as well?

Not without dramatically and massively increasing the amount of terrain in Tactics. That lack of terrain makes it the meat-grinder that is Tactics. If you put in enough terrain to actually have survivability, the game doesn't work the same way.

(Which is why I prefer Warfare; Tactics is written by French idiots.)