A brief overview of the best class / species combinations for admirals and governors. Intended for new players and not a comprehensive guide to all hero skills / interactions.
Hero skills mainly differ based on their species and class, and Heroes can either be assigned as a fleet admiral or a system governor; some combinations of species and class are better for these purposes than others.
For fleet admirals, the best classes are Guardian and Seeker. Guardians offer a bevy of fleet damage and survivability buffs, and a capstone skill that provides an additional extremely good tactics card; however, the Guardian skill tree has no mobility or utility skills and the hero ship itself only has 2 support module slots. If your ships are running 2 engines, the Guardian will not be able to provide cloaking or additional movement speed. Seekers bring mostly mobility skills, offering doubled warp (off-lane) movement speed, additional base movement, a few probes for scouting enemy fleet compositions, and 3 support module slots, allowing 1-2 to be used for fleet accelerators or cloaking modules. The other two classes have some minor fleet bonuses and more hero ship support slots, but are usually better as governors.
The best species for fleet admirals are Vodyani, Hissho, and Sophon, mainly because all three of these species have a +6 fleet movement skill as well as other combat buffs. Vodyani heroes have +40% energy damage and +25% health on fleet, Sophon heroes have +40% energy damage and even more movement speed, Hissho heroes have additional shield penetration, crit rate, and general damage. These species work very well as both Guardians and Seekers, as their species skills offer the mobility Guardian skills lack alongside even more damage buffs, and help make up for the Seeker's lower damage buffs while making them even more hilariously mobile.
Look at This Cutie
For system governors, Overseers and Counselors are the most generally useful classes, with an honourable mention to Guardians on very hot systems. The Overseer offers basically everything you want; more food, more luxuries and strategics, more industry, more happiness, even more industry and dust and food, everything that's good and they're useful for almost any system. The major bonus for a Counselor is forcing a system's happiness to maximum no matter the actual value, which is great for systems with lots of high-value low-happiness planets, but they also bring some influence, science, and dust. Guardians, as a governor, are all Industry all the time; with only two skills related to governorship but one of them being +30% Industry, they work very well as governors of Industry hubs but are terrible everywhere else. Seekers are generally bad governors.
Imperials and Primitives are the best species for industry focused systems. With many industry-boosting skills, including massive capstone industry boosts with senate effects, these species should be high priority heroes to pick up for governorship. A single Imperial/Primitives Guardian/Overseer on the right system can massively increase the amount of ships your empire can produce. Scavengers get a secondary mention for providing 10%-15% ship cost reduction which stacks additively with other ship cost reductions, so if you're playing an Empire that gets some of those e.g. Riftborn or Hissho it's very good value. Horatio heroes are, all of them, very good governors and senate heroes. +4 luxury production per deposit on a system, 33% more luxury production on system, and 33% additional luxury production empire-wide? If you have access to any good luxuries at all, that's a massive empire-wide boost to the speed and quality of your modernizations, making all of your systems significantly better.
Other Heroes Worth Mentioning
Any combination of class and species that I haven't mentioned is probably still good for something, just maybe not the best at it. Technologists are good as both fleet admirals and as governors of cold systems. Eusocials provide a lot of happiness, influence, and some food, as well as a few very good fleet admiral skills. Seekers with industry species skills can potentially stack a lot of assignment cooldown reduction and jump around to recently colonized systems getting them off the ground. Cravers are good for projectile fleets, and you can do some interesting things with the Craver capstone skill and a few anti-depletion Behemoth modules. But if you want to know which game-changing heroes you always want to buy off the market as soon as they show up? You want Vodyani / Hissho / Sophon Guardians / Seekers for admirals, and Imperial / Primitives Guardians / Overseers or any class of Horatio for governors.