First, Einstein didn't "invent the atom bomb." He did some of the work that eventually led to the development of nuclear weapons. But only basic theoretical parts, and even then, probably not the most important parts of that. His only real role was using his fame to get FDR's attention to become interested in the idea.
Second, there's obviously no clear answer, but a lot of people would say that the world would not have been a better place, because a huge conventional military conflict between the West and the USSR might well have occurred in the 1950s or 1960s.
But the basic question is probably ASB, because you'd have to lobotomize every physicist alive after 1900 to keep the bomb from being developed eventually.