A lot has been written about combat and crew strategies, and I've benefitted a great deal from reading up on those topics. But when it comes to upgrade strategies, the jury seems to be mixed. I've tended to get the most bang for my buck from shields, then doors. But I've heard arguments in either direction. Have also heard arguments (in varying degrees of persuasiveness) for prioritizing the other systems.

Can someone who's consistently beaten the game chime in on his or he preferred upgrade path?