Glucokinase has a higher Km than Hexokinase, resulting in lower affinity. Glucokinase is deployed after we eat a meal in order to limit the amount of sugar absorbed, resulting in a lower blood sugar. (G 6-P inhibits the activity of hexokinase.)
Hexokinases should not be confused with glucokinase, which is a specific isoform of hexokinase. While other hexokinases are capable of phosphorylating several hexoses, glucokinase acts with a 50-fold lower substrate affinity and its only hexose substrate is glucose. Glucokinase has a higher Km than Hexokinase, resulting in lower affinity.