Ok

For a noob these are pretty good.

Infantry are only good as comintern or Pan Asian

Nukes are niche

Rail road guns and arty are good and so are bombers

I like med tanks, mech infantry, cruisers, subs, sp aa, and armoured cars

Militia are also great, as well as tank destroyers

Heavy tanks are tricky to use properly

For me it's armored cars, regardless of map, doctrine or general composition of army.

Allied Doctrine:

5. Motorised Infantry - I really should use mechanised, but often it's too expensive, I like motorised because it travels at a decent speed and has most of the infantry's bonuses
4. Battleship - It can fight off all other naval units except the submarine effectively, and Battleships have incredible range, so you can shell land as well, which seems more effective than Artillery in most of my occasions
3. Light Tank - Outmaneuvers most other units, and overpowers other units during the early game, very good for encircling your enemy
2. Tactical Bomber - Amazing on this doctrine, decimates anything unarmoured on a high level when in stacks
1. Medium Tank - Best unit for breaking through enemy lines and actually fighting

Regardless of doctrine, no particular order:

Armored car: great to use as a scout/raider. Include them in a stack or detached them to go ahead and grab undefended territory. Great in the early game as well when infantry are the most common unit.

Interceptor: most players don’t build enough of them. Great to achieve air superiority and protect your ground pounders from enemy bombers. They’re comparably cheap and can also be grouped with bombers to spread the damage and extend the life of your bombers. Also good as a scout.

Cruisers: great all purpose ship. Faster than a battleship so you can choose when to fight, and cheaper so they can be mass produced. Resistant to bombers too.

Rocket artillery: great for bombarding enemy troops. You deal damage and take nothing in return. Better against light armor than regular artillery.

Naval bombers: Cheap and perfect for coastal defense. Perfect pack hunters, fan them out to quickly find your enemy then pull them back to group them and send them out again for the kill.