Enthalpy is the change in energy. A cold pack will react endothermically and enthalpy will be positive and a heat pack will have negative enthalpy. You cannot determine which has more change in enthalpy unless you measure the temperature change. Eg. a heat pack went from 25c to 35c will have greater change in enthalpy then a cold pack going from 25 to 20c because the net temperature difference is greater
