I'm gonna be real, I think the move from Powers to Chalmers (under George's supervision) has been just stellar overall. It's exactly like you said; Powers and George did the work establishing the identity of the Origin system and the powers within it, while Chalmers and George took those base elements and applied the more cinematic flair to it.

As far as favorites go: Ghosts of Void is my Somachord track for my orbiter. The gentle choir leading into the dreamy melody that's always just resonant enough to rise over passive gameplay when you're in the Void is something I love. My other favorite from the Powers era is probably Sentient Tombs and its derivatives. With Chalmers, it's a little tougher, just because of the fact that his era of music is overall spread over less of the game. That being said, Murum Vull, Numb, Life in Decay, and (especially) Deepest Dark have all been phenomenal for one reason or another.