[Nocturnal]

I don't look for a complete super ratio, I think that's a waste of time. Instead, I think in advance what I want each of my ship designs to do. For example, many of my ships are supposed to outrange the enemy, and stay just outside his firing range to dish out the damage. Those ships will get missiles and long range guns, and little to no armor (EMC I do give every combat ship, because it's so space efficient. I give combat sensors only to ships that use several direct fire weapons, including point defense turrets.)

For a missile ship, I'll give them loads of missiles and a handful of point defense cannons. No armor. Sometimes I'll escort these with dedicated point-defense ships that have about ten point-defense cannons, a combat sensor, and one "anti-ship" gun because otherwise they'll run into the corner and I want them to stick with my combat ships. These don't typically get armor.
Then there's the "Tank" type of ship. I'll give this one anywhere from 120 to 300 tons of [organic if I picked that] armor, and a few guns. Those have orders to move in close to the enemy to soak up the damage while the other ships shoot at them.

Carriers have at least 90 tons of armor to protect their cargo; they also have heavy guns and orders to behave as a combat ship. Noncombat ships typically recieve one organic armor and one lightning beam so they can beat enemy noncombat ships, and protect themselves for a little while if isolated.
I built an "armored dropship" class with 5020 cargo space, three fighter bays, and 270 tons of organic armor. This can take a planet without damaging its facilities, and if the planet isn't guarded by combat ships, it wouldn't even need an escorting fleet.
Fighters and troops never recieve armor (too useless on them) but may recieve one small shield if the enemy is consistently shooting them down.

My research path always goes towards good weapons first, then armor/shielding, and then specialized weapons like engine and weapon destroyers and shield-depleter boarding craft. Those Last use one heavy shield depleter, a tractor beam, boarding parties, a couple of point defense cannons and all the armor I can cram into them.

Remember: armor gets damaged first so the reason you're putting it on there is to protect the other components. You armor ships that need to be fast, or ships that have weapons you don't want destroyed, or any ship that carries close to its maximum cargo capacity into battle. It also should be applied liberally to ships that want to move in close-range to fire their weapons.

I do believe in "a good offense", but I also don't like losing ships. So I try to defend them enough to survive the battle (even if they're useless at the end of it.) I also try to design their defenses such that they'll be useful throughout the entire battle. My all-purpose "Orca" class battleship has 120 tons of organic armor, 4 [heavy I think] lightning beams, 6 parasites, and 4 point defense cannons. This is effective against many combinations of enemy ships because it can fight at any range. In my TDM game against the AI, one of these is conquering an entire front of advance by itself (With one troopship) and is at Legendary (40%) status. Because the organic armor heals itself after battle, he's never had to go back for repairs. But otherwise I'd just accompany it with an "Angel" class repair ship.
I recently designed a bigger model all-purpose ship with more armor and bigger weapons (enveloping acid globules so it doesn't need to get close at all.) I believe I called that a "Juggernaut".

In the army once they asked us what the difference was between armor and artillery. I jokingly answered, "armor has little guns and a big body, and artillery has big guns and a little body." The armor are supposed to protect the artillery, who dish out the damage.