I think J-10's canard is supposed to contribute lift in leveled flight, while the other design's (gripen/ef2000...) symmetric canards only provide control torque, does not contribute lift in leveled flight.
In zero canard deflection and zero AoA, J-10's canard shift both center of lift and aerodynamic center forward. Symmetric canards only shift aerodynamic center forward, does not effect center of lift.
I think it is only a minor design choice, J-10's canard produce more lift yet also produce downward draft downstream onto the main wings, so overall L/D might not differ. Just my two cents....