As I understand it (and someone feel free to jump in if need be), it goes something like this…
Fighter planes - max out defense, then max out attack. Agility/speed matters, but not as much as those other stats
CAS - max ground attack. Although there is a gimmick where you can make ‘fake’ CAS that function as fighters with the middle doctrine.
Bombers - max bombing.
For Navy:
Carriers - get at least 4, max the number of planes possible on them via modules/designers
Capital Ships - refit any starting ones if possible, using designer to give them speed or damage. Refits are cheap as long as you dont change out heavy turrets, engine, or armor. So give them secondary turrets and anti air. Also upgrade their targeting computer module in the process. Naval bombers go after capitals first, so make them function as floating anti air platforms
Heavy Cruisers - supposed the ideal super design is to get 2 lvl 1 heavy turrets, then max out secondary turrets. With screening bonus, they do a ton of damage
Light Cruisers - max out light attack
Destroyers - max out speed, they function as your meat shield. Supposedly a patch will make torpedo hit chance better, so maybe torpedos are worth considering
For tanks:
Too complex honestly. Also extremely dependent if on if youre playing singleplayer or multiplayer, and the rules youre working with. The general idea is to make sure your divisions are unpiercable, have around 8+ speed, and do a lot of damage while not being stupidly expensive
A very strong gimmick in single player is to create relatively cheap medium tanks, and put just one in a primarily infantry/artillery division which allows them to not be pierced by the AI while piercing anything the AI can bring to the table. Strong enough that its banned in MP generally.
Medium tanks are almost always the way to go, although there are some gimmicks you can use with Light tanks. Heavy tanks are trash other than their buggy inter-war version, way too expensive. Light tank variants like SPG and Tank Destroyers are very cheap, so you can work with that if you feel like getting creative.