I've done significant amount of research on the subject of perfect squad composition. I'll spare you all the mumbo-jumbo, but here's the result.

Best squad composition must have 5 armor, the rest is up to you, but there's one caveat to this: IF the forces are equal and full hp (i've done simulations with all possible permutations, this is the best result group).

So, here's the setup:
We have the attackers (10 armor, 20 range per squad) and defenders (10 armor, 20 damage per squad). Defender's fleets is cheaper on resources, but equal in workers use. These two are the min and max points, any other combination will yeld results somewhere in-between depending on which pint is closer.

Situation #1: Attackers outnumber the defenders. In this case damage units will deal less and less damage to the attacking fleet due to attackers taking out more and more defending units on round 1, thus reducing overall damage dealt on round 2, up to the point where attackers obliterate defenders completely on round 1 and suffering no damage at all.

Situation #2: Defenders outnumber the attackers. In this case defenders will eliminate the attackers with lessening losses as the difference increases, but the attackers will always get two shots of full ranged units damage before dying. One shot on round 1 (range advantage), and another shot at round 2 (alongside defender's damage units), thus will nearly always inflict losses on the opposing team (unless their total damage is less than half of armored unit's hitpoint value).

Situation #3: Defenders have exactly same amount of units (10 armor per squad + 20 of any other upgrade type). In thsi case no matter the proportion of damage and range, both teams will mutually destroy each other to the single last unit.

To sum up:
* Damage units are cheaper to build initially (best bang for your buck), but will require more resupply of units as the fights go, it'll be worse in the long run.
* Ranged units are pricier to build initially, but will suffer less loss and/or inflict more losses on the enemy forces as the game progresses, cheaper in the long run (cheaper maintenance).

And then comes the last point: unit experience. As your fights progress your units will rack up experience and their rank will increase. With ranged units by your side you'll be suffering less losses, and those will nearly always be only the armor, hence your ranged units will continuously rack up the experience. When running damage units you'll often find yourself needing to replace occassional lost damage unit here or there, thus losing the exp they might have accumulated and starting from scratch.

All in all, it comes down to how smart you use your units: it's the numbers and tie-breakers (spy attacks and nukes) that will decide the outcome of a battle.

That said, i, personally, run with the smarter choice of armor+range units, however i have many other uses for damage units, but that'll be my personal secret.

p.s. for the heaviest types (Heavy/Tanks/Cruisers) the ratio is 3 Armor, 7 others per squad (3/7), or, if you fancy mathematics, 3/7+3/7+4/6 per each of 3 squads (headache to maintain).

p.p.s. sorry for any mistakes, I'm a dragon, it's darn hard to type properly on these teeny-weeny keyboards of yours.

here are some graphs

(note: pro build = 10 armor + 20 range inf; damage build = 10 armor + 5 damage + 15 range inf)

When u outnumbered the enemy

This is the graph of performance (the percentage of the surviving units compare to the units participated in the battle) of the battles where u have 10 squads of choices against a certain amount of pro-build squads.



As u can see, pro builds and damage builds kill the same amount of units (one-rounded) when the enemy's units is 30% or less than the unit u sent.

When the enemy's units reached 40% and more, pro builds start to be more efficient, until the enemy's units is about 90% to equal to ur units, this is where damage units become useful, as battles dragged for 3 rounds and more.

Usually, u don't want to go 1 vs 1 with ur enemy, u always want to engage in an attack where u can outnumber the enemy the most to make sure u aren't losing too many units, which is why pro-build is the most recommended build.

However, there are cases where outnumber is not possible, or hard to achieve, big battles in eras with small alliance sizes (especially in solo) or the first 100 ticks of the era, this is where u should consider using damage.

When u're outnumbered

When u're outnumbered, unless u have xp advantages or other supporting tactics (agents, nukes, ions), u're pretty much dead. Hence, wat we should be concerned about is not performance, but the kill / loss ratio.

The graph is the Kill / loss ratio when u send a certain amount of squads at 10 squads of pro-build.



The all-range build is the most useful from 10% to 60%, however, the pro-build killed the same as all-range build at 70% to 100%. At 100%, damage build managed to survive the battle when all other builds end up as draw or lost.

If u planned to suicide into an army double ur army size, it would be more efficient if you send an all range attack, however, if u're just slightly outnumbered, using pro-build will be as efficient, with less resource needed for the battle.

>> tl;dr use all armor for ur army