I had the same question on one of my exams. First calculate the heat capacity of LiOH and then compare that value to the heat capacity of CaCl2. Use this equation:
q(heat of reaction) = -Ccal (caloromiter constant) x ΔT (temperature change)
Since the value of LiOH is negative the reaction is exothermic, and an exothermic reaction would be better used for a hot pack because it adds heat to the system. The bigger the heat of the exothermic reaction the better the hot pack is. so when you get your answer for LiOH compare it to CaCl2 then decide which is better. I hope this helps.