Hello.. what is strongest lightstone? i have all 4 red lightstone parts does there is stronger/better lightstones?

There isn't higher than red stones at the moment but you can get better stats on new ones, so always compare with the ones you have equipped whenever you get a new stone.
Also you can use multiple tablets for different occasions with stats that are suitable. For instance, pvp, guild wars... Etc

Best red lightstone cp15-15-15 pink lightstone coming in July probably