Reposting this from my FAQ thread:
UNIVERSALLY USEFUL UNITS
Eldritch-class basic jumpships (TL9) – Beta 1 proved that the Eldritch is the ultimate fighting machine. They move really fast and attack really hard and you can store them totally out of reach of retaliation by anything other than another Eldritch fleet when you're AFK (say, on top of your capital or in a nebula pocket). A big fleet of Eldritches is immune to missiles and will destroy most other ship types via sheer massed firepower without taking meaningful losses. The really successful empires were designed as fragile machines to turns most of their labor into Eldritches when not getting eviscerated by fleets of same. Wars between strong empires are hugely destructive since they are won or lost based on who can first-strike the enemy’s critical infrastructure with their giant Eldritch fleet. It’s very difficult to protect every critical planet needed to build a big Eldritch fleet from attacks by a similar fleet. Keep in mind that you will need LOTS of chronimium to build Eldritches. Store them all on your most heavily-defended capital when they're not in use. Keep consolidating them as your jumpyards build them.
Gorgos-class starfrigates (TL9) – Gorgos have 3x the cannon range of most other ships, so they will always inflict serious first-strike casualties while the enemy fleet is trying to get into range. Capital starships like the Gorgos have low attrition, too, which makes them even more efficient in real-world terms and you won't lose them very fast even if your empire falls apart while you're AFK. Importantly, when fighting Eldritches a Gorgos fleet seems to always destroy more labor than it cost to build, no matter the size of the respective fleets involved. This is not the case with most other ship classes, which have bad kill:cost ratios when they fight outnumbered. A fight between Gorgos and Eldritches will always be a victory in this sense even if all the Gorgos get destroyed. However, Gorgos move hideously slowly, so you still need Eldritches to actually wage offensive wars against other active human players. Gorgos are also vulnerable to jumpmissile strikes if you send them into enemy territory guarded by citadels. Build Gorgos on starship yards near your sector capitals, foundations, and hubs (if you use hubs) and constantly send them to reinforce these planets. Against planetary defenses a Gorgos fleet will always win without taking any casualties (even if the Gorgos fleet is tiny!). They are hard to kill, except by other Gorgos. You only need like 1 autofac for every 3 yards or so, unlike Eldritches which need like
3 autofacs one autofac for every yard. Oh yeah- starfrigates are also protected against missiles, although not quite as effectively as jumpships since fleet size is smaller. A big jumpcruiser attack on them would see missiles get through, but that would require that your enemy be building lots of expensive jumpcruisers and not, say, Eldritches to defend said jumpcruisers against YOUR Eldritches.
Armored Infantry (TL5) – I'm pretty certain these are the most efficient way to turn labor into infantry. It's not a bad idea to use transports to consolidate them onto your capitals every few days. Smart players attack individual infantry academies with transport fleets that contain overwhelmingly larger numbers of infantry (consolidated from multiple of their own academies). Overwhelming attacks will result in infantry quickly surrendering and the enemy actually gaining infantry. This is probably an oversight on the designer's part, but don't let yourself fall victim to this type of attack.
Imperial Guards (TL5) – Big empires MUST use the Law and Order doctrine and L&O capitals can only build defenses or Imperial Guards. Build Imperial guards. They aren't great fighters, but if you dump some of them (and no other infantry types) on the planets you capture, rebels can't win civil wars. Handy!
Reliant (TL6) and Warphant (TL9) transports – carry equal numbers of troops. Don’t mix transport types in an invasion- use all Reliants or all Warphants, keep them all in the same fleet, and usually you don't want move the transports to the planet until enemy defenses are destroyed. Warphants are significantly more expensive but are 50% faster; they also land faster which can be important if your enemy is actively moving jumpfleets around while you're attacking them. It's convenient to build your own transports, but after the early game it's sometimes be more efficient to not build any yourself, and just buy them from Mesophon or capture them from other players when you need them.
Helion and Vanguard explorers - Vanguards are not really a combat unit but they are cheap to build and are neccessary for mapping the galaxy in the early game. Helions are by far the fastest unit in the game and are as strong as a Stinger but cheaper (they do lack missile defense, though). Some players like to use them offensively, and why not- they don't require any components, so you can field a really huge number of them. This tactic may actually be effective against Starfrigates but I'm not really sure.
CONDITIONALLY USEFUL UNITS
Stinger-class basic jumpships (TL6) and Adamant-class jumpcruisers (TL7) – in the early game when you are trying to expand quickly and don't have that sweet chronimium locked down. Adamants are better against AI planets with lots of HEL cannons and autocannons. If you price everything out an Adamant costs about as much as an Eldritch to build but is way worse in almost every respect, so try to switch to building Eldritches as soon as your planets can handle it.
Minotaur-class gunships (TL8) – Minotaur fleets use much less chronimium than Eldritches and seem stronger on a labor-spent/labor destroyed basis, but they lack jumpships' protection against missiles and they are so slow that it takes a long time to assemble a gunship fleet together from multiple yards and send it against the enemy. You'll rarely if ever be able to attack a jumpfleet with a gunship fleet; jumpfleets can be moved away from attacking gunships and stored on fortified planets like capitals; and gunship attrition is too high to defend planets long-term against jumpship attack (Gorgos are better for this because of their lower attrition and first-strike capability). From their stats, Minotaurs look like they should perform better against Eldritches than they actually do most of the time, IMO.
Defiance-class starfrigates (TL6) – Gorgos' poor country cousin. The only ship with range>10 that doesn't require advanced resources. Long range means they get first strikes against all jumpship and gunship types and outrange cannon-type defenses. They are a less cost-effective use of labor than Gorgos, but they are a little easier to build early on and/or in spots where you don’t have enough planets to run a chronimium economy.
Jumpmissiles (TL7) – Protect your key planets with citadels if you are worried about an enemy with a strong starship fleet. They can destroy multiple weak units with a single hit, but seem to be most efficient on a labor/destruction basis when fired against starships, especially moving fleets- if a fleet is stationary and gets hit by jumpmissiles, the missile protection of jumpships or starfrigates will shoot the missiles down. How do you guard citadels against jumpships, though? Well, you can use gunships (high attrition), lots of starfrigates (expensive), armored infantry/exotroops (attrition, have to tediously keep dropping them off), or cannon-type defenses (building defenses means building fewer jumpmissiles).
HEL cannons (T4), plasma towers (TL8), hypersonic missiles (TL6)- mostly in the early game. Hypersonics have double the range of most ships and can even cause problems for small jumpship fleets. If you have a planet with spare labor (e.g. a hub or foundation) you might as well dump some of it into defenses. Really big late-game empires can amass Eldritch fleets that are so large they will steamroller even the strongest planetary defenses without taking significant casualties; defenses become mostly obsolete in the late game.
Cyclops-class starfrigates (TL9) – use them like Gorgos for defending key worlds in nebulas. These can also be bought from Mesophon for extortionate sums. Not as labor-to-killin' cost effective as Gorgos to build. The ONLY ship in nebulas with a longer cannon range than Eldritches. Do not require chronimium, which means more chronimium to build Eldritches. They are much faster than Gorgos so you can go on the offensive with them, especially against AI planets and in dark nebulas where player enemies might not see them coming. A funny trick is to suddenly buy an enormous number of them from a Mesophon planet and sic them on the nearest nebular sector capital or other weak point; sell captured ramjet parts to Mesophon to buy even more Cyclopses. Other players will get wise to this pretty quick though.
Undine-class jumpcruisers (TL10). One way to dodge the graviton launcher bug is to build a small number of these at each of your TL10 jumpyards. They are not as efficient as Eldritches in 99% of combat situations though. May be more effective against Gorgos than Eldritches in some cases, but this needs more testing. They have to be built at TL10 worlds, which have complex penalties associated with them above and beyond those of TL9 planets that can build Eldritches (TL-associated labor bonuses and consumer goods demand penalties are a can of worms that I'm reluctant to open quite yet).
Sirius-class gunships (TL5) – Their cannon range is half that of the Eldritch so they get eaten alive by them. Also slow. May be briefly useful in the early game to defend against aggressive players who use Stingers or Helions.
Hammerhead-class nebular gunships (TL5) – A gunship that fires missiles. Stats are actually identical to the Undine but it's slower, cheaper, and can't leave nebulas. Useless against Stingers, Eldritches and Cyclops. May be situationally useful in the early game. You are better off buying or building Cyclopses if you can.
Cerberus-class nebular gunships (TL8) – like the Minotaur but seem to be generally less effective against Eldritches despite being individually stronger. This is because they are more labor-intensive to build - smaller fleet size means they are more likely to not be able to inflict meaningful casualties against a giant jumpfleet before being destroyed.
Exotroops (TL7) – Not as efficient to build as armored infantry and require more dedicated planets. Don’t require as many transports, though. Exotroops are unusually good against basic infantry but basic infantry are lousy anyway.
Basic infantry (TL1) – less efficient to build than armored infantry even though they don’t require any resources to build.
Autocannons (TL5) - They only seem to attack one enemy wing at a time, while an unlimited number of wings can attack them all at once.
All Starcruisers- Victory, Megathere, Behemoth, Typhon – TOTALLY USELESS. Trust me on this one. They're really expensive and can't fight jumpships or starfrigates at all.
Manta-class nebular starfrigates (TL6)- a starfrigate with no range advantage against jumpships or gunships. USELESS.
Battlestations – starcruisers that can’t even move; also require heavy missile launchers, a resource built at starship autofacs. Those autofacs could be building Hellfire Cannons for more Gorgos.
GDMs, armored constellations - offer close to no protection against jumpship attacks, which are 99% of the attacks you can expect other players to launch against you.