I usually use light dragoons if I have that choice.

They can shoot up their intended targets before a charge. I group them in pairs so one is always on the enemy flank and they are caught in a crossfire. They can take on most any unit in that respect.

I mainly use them early to take out the enemy artillery and then to support the infantry by attacking the enemy’s rear when they close for melee.

Squares cause too many casualties to charging cavalry but their divided fire power make forming a square against dragoons suicide.