It seems that tec loyalist is better than rebel in every possible game area (except maybe titan, although that is subjective). The TL vette is the best in the game, allowing players to snipe caps with impunity. They also get the best late-game techs, with nova deregulation, double SBs, and the various defense boosts having the potential to be game-changers.
On the rebel side, the only notable unique research is TAR, which has been severely nerfed since the game's launch. Now it is at best a situational ability, prioritizing horizontal expansion over vertical expansion. I've even seen players beat eco's using TAR, because the latter spends too much on planets instead of an trade ports.
Thoughts??