Actually, while Starcraft comparisons don't work that well in Sins, the Vasari are closer to the Protoss than the Zerg. All their ships take more fleet supply and have weaker stats at first, but they have many unique abilities and technologies that can totally change the game and give them benefits other races can only dream off (shield piercing missiles, phase stabilizers to jump between unconnected planets etc.).
The TEC are the simplest race to play as. They get access to trade early and have the best overall economy and production base. Their ships are very cost effective but tend not to have the powerful abilities the other factions rely on. Because of this its very hard for the TEC to win a fair fight, but they don't need to, they should be fielding more ships and are the perfect race to win a war of attrition.
The Advent also have very good military ships, though they have the weakest economy as their civic techs tend to focus on culture, which has many effects but none is particularly good on its own. By themselves their ships have good damage but are somewhat fragile and shield heavy, but you won't be using your ships by themselves. The Advent dominate by using synergies between their various units to massively buff themselves or reduce the effectiveness of their opponents, making the whole fleet far more dangerous than the sum of its parts combined. Its not uncommon to see fully developed Advent fleets rip apart almost equally sized but badly managed fleets with almost no casualties.
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