One of the many problems with these types of questions is how you define greatness? Is it best peak performance, most awards/records, winning/championships, highest average performance over the length of a career, dominance vs skill, image/perception, impact on the league?
When we talk about who the best is, we all weigh these different factors differently. Selecting the best ever would be relatively easy if we were all applying the same standard (winning=russell, image=mj, longevity=kareem?). So what the conversation really is about is what determines greatness, not who is the greatest.