Also what choices did you find hardest to make and do you have any regrets?
As always, any references to particular missions should be properly spoiler tagged.
Protoss Research
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Vanadium Plating (armor upgrades increase life 5%) (29)
178 total votes
Your vote: Protoss Tier 1
(Vote): Ultra-Capacitors (weapon upgrades increase attack 5%)
(Vote): Vanadium Plating (armor upgrades increase life 5%)
Micro-filtering (refineries mine gas 25% faster) (74)
160 total votes
Your vote: Protoss Tier 2
(Vote): Orbital Depots (supply depots build instantly)
(Vote): Micro-filtering (refineries mine gas 25% faster)
Command Centre Reactor (CC can build two SCVs at once) (27)
141 total votes
Your vote: Protoss Tier 3
(Vote): Automated Refinery (refineries no longer need SCVs)
(Vote): Command Centre Reactor (CC can build two SCVs at once)
Raven (25)
127 total votes
Your vote: Protoss Tier 4
Orbital Strike (Barracks units arrive by drop pod) (14)
125 total votes
Your vote: Protoss Tier 5
(Vote): Tech Reactor (addon that combines reactor and tech-lab)
(Vote): Orbital Strike (Barracks units arrive by drop pod)
Zerg Research
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Fortified Bunker (bunkers gain +150 life) (87)
182 total votes
Your vote: Zerg Tier 1
(Vote): Strike Turret (bunkers are outfitted with a turret)
(Vote): Fortified Bunker (bunkers gain +150 life)
Planetary Fortress (PF upgrade for command centres) (59)
150 total votes
Your vote: Zerg Tier 2
(Vote): Planetary Fortress (PF upgrade for command centres)
(Vote): Perdition Turret (a flame turret that hides when out of combat)
Predator (anti infantry vehicle that does area shock dmg) (33)
125 total votes
Your vote: Zerg Tier 3
(Vote): Predator (anti infantry vehicle that does area shock dmg)
(Vote): Hercules (massive dropship with fast unload)
Cellular Reactor (specialist units gain +100 energy & +100 max energy) (40)
118 total votes
Your vote: Zerg Tier 4
(Vote): Cellular Reactor (specialist units gain +100 energy & +100 max energy)
(Vote): Regenerative Bio-steel (mechanical units regenerate health)
Hive-mind Emulator (structure that mind controls Zerg units) (48)
116 total votes
Your vote: Zerg Tier 5
(Vote): Hive-mind Emulator (structure that mind controls Zerg units)
(Vote): Psi Distruptor (structure that slows Zerg units)