Curly hair is often dry, so most conditioners made specifically for this type emphasize moisture. Hydration keeps curls from turning into frizz and stops breakage.
If you have kinky hair, the best conditioners I’ve found are Oyin Honey Hemp and Curls Coconut Sublime Moisture Max Conditioner. I like Oyin the best because it’s handmade with natural ingredients, smells wonderful, and makes my hair so, so soft. The Curls conditioner is really wonderful and effective, too, and costs a little less.
For other curly types, I bow to the curl experts at DevaChan. Not only is the DevaCurl One Condition one of the best conditioners for dry curls, it also comes formulated specifically for blondes, brunettes, and those with extra dry/damaged hair. I also love the B’Leave In conditioner for keeping locks hydrated on the days between washings.