Which pool chlorine to buy???

i am confused about which powdered pool chlorine to use..i have been buying the so called best one from the pool shop but it is very expensive...it has stabilised pool chlorine in it....560g/kg avaliable chlorine..present as sodium dichloroisocyanurate?..... where the supermarket one is half the price but has 750g/kg of some other type of chlorine ...what to do???