Probably Corsair or Commodore difficulty. Although I must admit that these difficultly levels are unchanged from City of Abandoned Ships (COAS) settings and therefore are also prone to some things still not ideally balanced, but I think they are the closest to providing a proper level of difficulty to most situations.
Also, even though I do recommend the ERAS II mod, we have fixed most of the problems in our version of both GOF 1.2 and COAS too, if you'd like to try them.