Stellaris ship design

Early game loadouts are somewhat irrelevant, numbers are the most important thing in early clashes unless you get lucky on certain rare techs from space-borne aliens, this changes around the time you unlock cruisers.

To look at weapons:
Missiles are worthless, they're cool and all but they're utterly worthless due a myriad of issues. They can be shot down effortlessly by point defense guns and any missiles en route to a ship when it dies will disappear into the ether never to be seen again wasting a lot of DPS. Avoid them at all costs.
Energy torpedoes are the sole exception as they are completely immune to point defense and are capable of laying out serious hurt to shields making them more or less mandatory on late game corvettes.

Kinetics are excellent, they're effective all round and at all stages of the game due to moderate bonuses against both shields and armour. The real stand out kinetic weapons are kinetic artillery, a L slot exclusive gun that is hands down the most effective L slot weapon in the game due to the standard kinetic bonuses to shields and armor, exceptional range, and good accuracy, and flak cannons which are long range M slot point defense weapons (unlike regular PD which is limited to its own specific PD slot) and also very capable of putting the hurt on corvettes and destroyers. Autocannons deserve an honorable mention as they boast great DPS but they're somewhat held back by limited range and a lack of a damage bonus vs shields and only a small bonus against armor.

Energy weapons are also good, their regular line isn't quite as good as kinetics due to a small penalty against shields, however they boast superior accuracy and excellent damage vs armor. Plasma is where the real power lies in energy weapons, capable of practically ignoring armor entirely to do unmitigated damage vs hull they are THE weapon for killing high armor targets such as cruisers and battleships. Disruptors are arguably of use as they crush shields but honestly they're just not worth it as they become useless once hitting hull unlike the more flexible kinetic weapons and energy torpedoes.

Strike craft are contentious. Bombers are completely garbage for sure, but some people get a lot of use out of fighters as they launch at extreme ranges, shoot down missiles and are capable of dealing not insignificant damage to corvettes. They're effectively an 80~ range PD weapon that can also kill corvettes, the trade off is they're vulnerable to PD themselves which can result in them dying and they don't replenish until your fleet leaves combat. I personally like them, you may not. Also remember they launch 8 per hanger but their listed stats are per strike craft, so don't judge them entirely off that.

XL slot weapons are cool as fuck but ultimately just not as good as their worth in L slot weapons, making them flashy but not too useful. Especially arc emitters, only use them if you have a gambling problem.

On ship design:
Battleships are NOT a shitty meme and completely unusable garbage like some people say. They're just simply not as cost efficient as cruisers, take much longer to replace should you lose one and are incapable of hitting corvettes. They're specialist craft designed solely for killing other battleships and cruisers. For optimal play whenever the question "should I build a battleships?" comes into your head, the answer is no, build more general purpose cruisers instead. It must be stressed though, THIS DOES NOT MAKE THEM BAD, it just makes them sub optimal they're completely fine to build if you're not trying to min-max and are capable of performing in a mixed fleet, just don't spam them and try to rely on them solely, like you can with cruisers.

Shields and armor are both important, but it varies depending on ship size. Destroyers and corvettes get basically no use out of armor and rely more on evasion to get by, max their shields out and throw a capacitor on them to enable in combat regen and you're golden. Cruisers and battleships are different, they have dick for evasion and are going to take a lot more shots, thankfully they have higher inherent armor and bigger utility slots, armor soft caps at 75% so shooting for that and filling the rest of their slots with shields is an alright idea for battleships, however 75% is an unfeasible number to reach on cruisers without neutronium ore boosting your values by 20% and pretty much requires your components are at max tech level 40-50% is much more reasonable for cruisers, when in doubt just stick more shields on it and they'll hardly ever be wasted. Armor hard caps at 90% but the designer won't factor in buffs like repeatable techs and strategic resources so plan around that and don't waste too many slots on armor when it might be wasted.

Here are the armor caps and base values for those interested

			Base	Soft cap (75%)	Hard cap (90%)
Corvettes	2		52.5			73.5
Destroyers	12		60.375			84.525
Cruisers	30		76.125			106.575
Battleships	80		107.625			150.675

Some sample ship loadouts:
Corvettes;
Energy torpedo and plasma/autocannons in the S slots, utility slots can go two ways, either naked with an afterburner to be a cheap disposable source of high firepower, or shields and a capacitor so they can survive more hits and be a more persistent but more expensive pest

Destroyers;
Gunboat style. Go with the L slot front and stick a kinetic artillery in it and M slot stern with plasma. Fill utility slots with shields and a capacitor. Destroyers get high inherent bonuses to tracking so an L slot on them actually has a chance of hitting small ships while still being capable of dealing serious damage to large ones and the plasma will burn through hull FAST after the artillery has shredded the shields at long range.
Screening style. 2S 1M slot front and the 2PD stern. Fill all the non PD slots with plasma and the standard shield utility fit. The ship exists to swat corvettes and missiles down like the irritations they are but will pretty much tickle any larger ship. If you REALLY need PD you could also use the PD front but you'll probably never need it that much and it's a waste of a ship when no missiles are about then.

Cruisers;
Ultimate cookie cutter. 1 L slot front M slots on the mid and stern. Kinetic artillery in the L slot and plasma everywhere else, try and get armor up to a decent amount, maybe 60%+ and then slam those shields. This ship is THE most cost efficient all rounder ship in the game. If massed it can take on pretty much anything and win. Plasma ruins cruisers and battleships and there's enough of it that while it won't hit corvettes often shear numbers will make up for it. Optionally you can replace 1 M plasma with a flak for some limited PD.
Defensive all rounder. M slot front, PD mid section and M slot stern, plasma in the M slots and fighters in the hanger, you know the drill on utility by now. This is less capable offensively than the cookie cutter but better defensively, completely removing the risk missiles and bombers might pose to you and putting serious damage onto corvettes. Don't mass these keep their numbers low, they're there to protect your big hitters not replace them and they do the job admirably. A personal favorite of mine

Battleships;
Ship of the line. All L slots. All with kinetic artillery. Armour to about 75% and then stack shields and caps. This thing exists to make your opponent regret bringing cruisers and battleships to the fight with crippling long range firepower. Don't expect it to ever hit destroyers or corvettes though, but you brought some screening ships right?
All rounder. L slot front, 2M 2L midsection and 2M stern. As usual kinetic artillery in the L slots and plasma in the M, the usual in utility. Less specialized and more able to hold its own when pestered by smaller ships than the ship of the line while still maintaining good long range damage output, unlike the ship of the line you could easily make these the core of your fleet, if you have the economy to.

This should be enough to get someone with no idea about ship design on their feet. Feel free to post about anything you disagree on in the thread. I'll change and update this as required.