The amount of damage dealt is calculated as the triggered ability resolves based on the creatures you control at that time, including Basalt Ravager itself if it’s still under your control. You’ll always use the greatest number possible. You don’t need to choose any creature types. For example, if you control a Giant Wizard, a Giant Warrior, an Elf Warrior, and a Kor Warrior at that time, Basalt Ravager will deal 3 damage.