The most different between Qira`at is in the letter hamza as we don`t pronounce it in some qira`at and pronounce it in others,also in the time of (mad) (mad is the time of pronouncing letter alef or ya and it is some times 2,4or 6 harakat)and when we do mad ,when we don`t,and when we do tafkhem for some letters and when to do tarkik for it like letter ra and lam ,in some qira`at letter ya is pronounced as alef in some words and in other it is pronounced as ya all the time as in word يخشى it pronounced as yakhsha in some qira`at and pronounced as yakhshy in others,there is many other defferents ,Prophet Mohammed peace be upon him and his companions recited Quran with all qira`at so they are all right ,just it is the dialects of Arab at this time as they pronounce the same word in different ways.