In my opinion, there's just to much going on in an average game to say that one aspect is more important than another. Pairing up multiple strategies is normally more effective from what I've seen. I remember one game, I was able to use a defensive Inspector and the mobile Smuggler to neutralize a large attacking force. My opponent had launched several subs at 2 of my outposts. Using the 2 previously mentioned specialists, plus my Queen for her shield boost, I was able to bounce between my 2 outposts and lose only a few drillers. Had I focused on just defence, I would have lost one of the outposts, with just mobility I didn't have enough drillers required to fight off both attacks. It was only through pairing both aspects that I could fend off the assault.