I am trying to make a basic tier list of regiment types in terms of strength vs cost, versatility and playablity. I would love to hear your input on this, if you think I miss ranked something or would like to question why I put something in a location do let me know.

No:
Siege Infantry
Salvage and Recovery Regiment
Artillery Regiment
Heavy Reconnaissance Regiment

Maybe:
Rapid Reconnaissance Regiment
Drop Troops
Close Assault Regiment
Hunter-Killers
Guerrilla
Super-Heavy Armored Regiment

Good:
Rough Rider Regiments
Grenadiers
Armored Regiment
Line Infantry
Light Infantry

Yes:
Reconnaissance Regiment
Mechanized Reconnaissance Regiment
Mechanized Infantry

Thanks for reading.

I'm curious what your criteria were. For example, for me, Siege Infantry was always appealing because of the extra ammo they got.

So I cannot agree or disagree with this ranking, as I don't know what you were looking for.
Edit:
My personal ranking would probably go something like this:

No:
All vehicle regiments save Super-Heavy, Hunter-Killer and the one that gives everyone a Sentinel.
Rough Riders

Maybe:
The exceptions from the vehicles
Close Assault
Guerrilla

Good:
All the other infantry options, save for:

Too good:
Grenadiers (particularly with Vanguard)

The vehicle stuff just works too badly / needs a lot of fixing for those who don't fit in the vehicle.
Close Assault and Guerrilla (tho mostly CA) are just weaker than the other infantry options whereas Grenadiers get too good equipment. Gets ridiculous if you upgrade their armor. Vanguard just makes them flat-out better mechanized infantry and those are already very good.

I put the Drop Troops as Good. But I tend to be the type of gamemaster who throws out dice rolls and or the book if it gets in the way of telling good stories.

Yeah, the Aeronautica checks are tough, aren't they?

But all the infantry options can be made to work well enough, even the two that I think are underpowered, honestly.

Yeah. Those checks can be painful. I agree that all types can be me made to work with a little fore thought and on the fly story telling.