From what i know and from what a studied, the Collector is the strongest person in his Universe, but im pretty sure he cant atomise some one by breaking them atom by atom and can go anywhere in the multiverse/dimensions/Realms/Realities
Yep, thats the Traveler , but since i dont know exactly where and in what universe the Collector lives in or if he is even capable of travelling in the multiverse, I can't say that the Traveler is stronger than the collector