I want to take a look at the tech tree for a general balance discussion.

For this discussion, I'm only going to focus on the techs I consider a cut and away better than the rest. In other words, if someone didn't pick them up they would be a good bit behind someone who did. I think there are more, but these are the techs I think are the most powerful.

Colonization

Xeno Biology: An extra 35% growth is a key multiplier early game. While planetary improvement could be lumped into that category, it is so commonly taken that I don't mention it.

Enhanced Production: Remember this is not +1 manu, its +1 production. Early on, its effectively 10 turns of free growth. Later on its worth at least 1 if not 2 population, especially since it doesn't require approval. This is biggest force multiplier you can get early game.

Engineering

Hyperdrive Specialization: +1 moves forever. Extremely good. Great for early scouting, avoiding pirates, helps tremendously in the colony race. I will say this is the lowest of my OP techs.

Interstellar Logistics: 10 logistics that early in the game is very very powerful. In early war rushes I can mass together death fleets that enemies have a hard time dealing with.

High Capacity Hulls: Every mass reduction tech pales to this one, because it effects them ALL.

Conversion / Influence/ talky stuff

Supportive Population: +4 passive morale is a massive boost, especially now that morale assists with production.

Galactic Governance: +20% production. All production. Effectively your civilization's economy becomes 20% better...period.

Interstellar Democracy: Like galactic governance, but more awesome (30%). Further down the tech tree, but still extremely strong.

Technologist Party: Research is always good, and +30% is a massive bonus. Better than going down the research tree in colonization for a good stretch. Combined with the previous 2 techs, you have increased your entire research economy by 80%...as if every planet get 3 free research labs.