In your opinion, what is the most effecient unit for every tech branch?(Or rank them)

Depends on the doctrine.

They have different purposes and it's kindof nonsensical to "rank" them this way. It would be better to create categories based on how the unit is used (for what strategical purpose), as follows:

Heavy fighting over key points:

Artillery = RailRoadGuns > Infantry = Heavy Tank = Commandos > Militia^1 = Tank Destroyer > Anti-tank = Mech Infantry

Quickly eliminating exposed armies, before they can merge into the enemy's main army:

Attack bombers^5 = or > tactical bombers > mot infantry^2 > light tanks = medium tanks > armored cars > mech infantry = rocket^3

Scouting and conquering all the exposed territory:

Mot infantry = or > armored cars > mech infantry^4 = light tanks = or > medium tanks

Against planes:

Interceptor > rocket fighter >> Anti Air = SP Anti Air >> Infantry > everything else

Trolling:

Flying Bomb > Aircraft carrier = paratrooper > SP Anti Air = Nuclear Bomber > Nuclear Rocket^6 = Heavy Tank

Notes:

^1 - militia is super fast to produce, the only reason it has a good position is because it's the best unit to spam quickly if an enemy stack is coming at your city, your army can't return to defend in time and you really need to save the city, so you spam militia out of it to fight and delay the invaders until your actually powerful army comes.

^2 - I rank mot inf very high in personal opinion, but its compromised by the fact it costs food (which you need for Recruiting Stations and you cant buy extra food cause the prices are usually high on food in the market; in this regard, armored cars are more convenient)

^3 - rockets only for a specific purpose: destroying very low-hp, high value targets which you can't hit with bombers. For example, if your enemy has a 10-stack of artillery sitting and bombing you, and hes guarding it with 20 fighters, you cant send bombers at it, but you can decimate it with rockets. Artillery is so low-hp that the amount of destruction per rocket is worth the cost.

^4 mech infantry has a terrain bonus in cities (if I remember correctly). This is usually good for conquering.

^5 attack bombers are more than decent against ships. This is additional convenience, you can use them to sink convoys

^6 nuclear rocket is unfortunately a bit useful, so it can't get a higher trolling rank.