Green antifreeze or coolant as some call it.

Copper radiator?
Copper heater?
Open overflow, or relatively open flow tank?
Use 'conventional' green.
Conventional uses inorganic corrosion inhibitors.
These provide immediate protection.

All of the others are some form of organic acid technology, or hybrid organic acid technology. This includes most if not all 'universal' antifreeze.
OATs and HOATs need some time in use to be effective. They work best with closed systems. Most do not have protection for soldered copper and brass as a important goal of their corrosioninhibition packages.