Very short guide = Very short introduction

The basic idea is to research technologies that lead to good repeatable technologies, while removing as much undesirable repeatable tech as possible from the pool of available research. Enjoy, and please leave feedback.

UPDATED for 1.4: Both Physics and Engineering are viable for endgame weapons.

The best repeatable techs are Energy Credits, Energy Fire Rate, Energy Damage, in that order. EC allows building ships over the cap as well as support more science buildings, Fire Rate flat out increases DPS, Damage wastes some DPS on overkill damage.

PreReq Techs:
UV Lasers (Lasers III) (leads to Energy Weapon Fire Rate/Damage)
Shield III (unlocks Shield Health and is a prerequisite to the OP Capacitor)
Power Plant IV/V (unlocks Energy Credits)

Undesirable Techs:
If you're going for Engineering instead of physics, don't get Physics II - that will unlock building construction cost/time repeatables. Obviously, a physics focused empire can't skip this tech.

Notes:
Technically Gravitic Sensors leads to the useless +10% planet sensor range tech, but I find the accuracy bonus from sensors too useful to ignore. The resource buffs are nice if you can get them as well.

End Result:
3 desirable repeatables, 1-3 undesirable repeatables. Once you research +1 Research Alternatives, you are guaranteed a desirable repeatable. Engineering focused empires that don't research Physics II are guaranteed to get Energy Credits, arguably the best repeatable, every single time.

There are too many good repeatable techs to count, and which are good or bad vastly depends on playstyle. +1 Core Worlds is undoubtedly the best, so it's rather unfortunate that unlocking it requires unlocking 3 other less useful repeatables.


PreReq Techs
Artificial Moral Codes (-10% resettlement) -> Eddict Duration
Adaptive Beauracracy (eddict cost, +2 leaders) -> +1 Core Sector, Sector, Leader, Leader Cost
Border Range -> Border Range
Uplift -> Leader Lifespan
Nueral Implants -> Slave Mineral Production

Undesirable Tech
Combat Training (army upkeep): Leads to Army Damage and Army Health.

Notes
The nigh useless +5% food tech is the unavoidable cost of getting decent farms. On the bright side, if you research this enough you can get away with fewer food tiles. Due to how Society techs branch the only undesirable tech than can be avoided forever is the army upkeep one, the rest have prereqs that are vital.

Due to how many of these techs rely on micro (leader capacity, eddicts, slavery, core sectors...) it might be a bad idea to focus too much on society research if you don't plan on taking advantage of all the influence by microing your planets.

If you want to rush colonization techs, avoid Genome Mapping (food production, leader lifespan), Planetary Unification* (influence), and Doctrine: Space Combat (naval capacity), as they each unlock 2-4 more techs, some of which unlock 2-3 more techs... I highly recommend a government with at least one extra research option if you plan on rushing colonizing all planets for this reason.

*I might be the first person to suggest that getting Planetary Unifcation early might be a bad idea. Now you know why it takes so long for the RNG to give you colonization tech.

The best techs are Minerals, Kinetic Fire Rate, Kinetic Damage, Ship Health, Ship Armor, in that order. Minerals lets you get away with fewer mineral planets, so you can have more energy planets, allows rebuilding fleets faster, and helps sectors build. Kinetic Fire Rate is better than Damage, due to overkill. Ship Health/armor is nice, but if you have Kinetic Artillery spam with a fast fire rate you will ideally be winning the battle before your enemy gets close enough to start hitting your capacitor+shield defense.

PreReq Techs
Mineral Processing Plant II -> Minerals
Gauss III (Railguns) -> Kinetic Damage, Fire Rate
Spaceport IV (Destroyer Assembly Yard) -> Ship Health
Armor III -> Armor

Undesirable Techs
Missile III -> Missile Damage, Fire Rate
Station II -> Station Health, Station Damage
Basic Fighter -> Strike Craft Damage, Fire Rate

Notes
That's a lot of undesirable techs. A government with at least +1 research options is needed to permanently avoid these useless upgrades.

My justification for declaring missiles, stations, and fighters undesirable in the late game would require it's own section, and listing all the flaws of fighters would require an entire guide in and of itself. Hopefully 1.3 changes this. 1.4 changes this. 1.5 changes this.

End Game:
3-5 desirable techs, 3 techs that lead to undesirable tech, 6 undesirable repeatables if you research everything. Get an early +1 Research Alternatives from tech or a government to avoid the bad choices. Alternatively, research the debris of an empire with missiles III once - and never research their debris again until they've moved on to missiles IV or V. Techs partially researched from debris are taken out of your tech pool permanently (unless you scan enough debris to get the tech by accident).

It's not just Tachyon's, Physics is OP, period. It is the only tech tree that doesn't require a special government type to avoid researching undesirable tech.

Colonization Techs only feel rare because because 3 of the best early techs actually unlock over a dozen techs, reducing your odds of pulling a colonization tech. You may want a "+2 research option" government, +4 with advanced government forms, if you want one tech in particular.

Engineering has the most undesirable techs. A "+1 research option" tech or goverment is the only way to guarantee preventing the unlocking of multiple useless repeatables that will crowd out the good options.

Be careful with research debris. Accidentally researching Gauss III or Missiles III as a physics focused empire, or Missiles III or Lasers III as an engineering focused empire, will unlock undesirable repeatables.