Which is best, a leave-in or rinse-out conditioner?

They're different. Rinse-out conditioners treat hair by coating and filling in the the hair cuticle, making the hair stronger and more manageable. Leave-in conditioners are lighter formulas designed for daily maintenance and should be combed through towel-dried hair. Leave-ins coat the hair to add shine, reduce friction to prevent breakage and restore moisture and manageability. Heat protection sprays are leave-in conditioners that prevent moisture loss due to heat-styling. Another type of leave-in conditioner, a curl boosting spray, adds moisture and elasticity to the hair to encourage the curl pattern and add bounce.