Races in Sins Of The Solar Empire are not extremely specialized (like in, for example, starcraft), each of them is is using same types of units (long range frigates, heavy cruisers, carriers etc.) almost the same way, differences between races are far more subtle. Each faction is slightly specialized in something, each of them also has capital ships with unique abilities... there is short description of main advantages/disadvantages:
TEC:
- Strongest Trade in game
- Strong Ore extraction
- Strongest Ships Hulls/Armors (per cost)
- Good use of pure force
- Super strong damage dealers (Marza Missile Barrage, Kol Finest Hour...)
- best colonization upgrades
- strongest planet development
- weakest fighters and bombers
- lack of tactical depth compared to other two races
- lategame may be problematic against Advent and ESPECIALLY Vasari
Advent:
- Best shields in game and units abusing them (Iconus Guardian)
- Best fighters and bombers in game, strong carriers
- Tons of synergy between different units making mixed armies very strong
- Best culture spread
- Best colonizer capital in game (mothership)
- very strong weapon upgrades
- psi manipulation as integral part of many skills/abilities
- you can easily build strong and very versatile army
- best intelligence (based mostly on culture spread)
- hot and cute unit voices
- worst resources extraction
- weakest armors and hulls
- problems with early eco, if you do not use mothership
Vasari:
- Strongest and the most cost effective lategame fleet in game
- best resources extraction in game and easiest way of capturing neutral asteroids
- Only Starbase in game able to move (no phase drive OFC)
- best hull regeneration
- all units are more expensive but slightly stronger then TEC/Advent equivalents
- phase manipulation: phasing out enemy ships, disabling drives, gravity well radius needed to jump manipulation etc
- phase stabilizers allowing you to jump between unconnected grav wells and summoning strong fleets for minimal resources
- longer you play, the more cost effective your ships are (truth for all factions, but Vasari benefit this rule far more)
- strongest superweapon in game (place phase stabilizer allowing you to attack from any planet AND disable EVERYTHING ENEMY HAS in entire gravity well...)
- weakest early game fleet (units are significantly more expensive but only slightly stronger then Vasari/TEC equivalents)
- you are forced to capture neutral resources early game or you have an disadvantage
- worst colonization upgrades (to volcanic planets...)
- low cost-effectiveness of units during early-midgame
- Lack of strong AoE damage dealers (like TEC Missile Barrage or Advent Cleansing Brilliance)
- unit voices are annoying after few hours
I've started as TEC, then switched to Advent and now I play Vasari-only.