For all the talk of who is historically better, can we use the Bill Simmons pyramid as a starting point? If you've read his Book of Basketball, you understand he did a significant amount of research to come to his list. That said, any list like this includes some bias. But at least this generally puts the right players into the right groupings. I saw someone say Karl Malone was ahead of Kobe. Umm, no.
Simmons HOF Pyramid - Top 96
Edit : LeBron is the variable here. The list is a couple of years old, so the assumption has to be that LeBron has moved up from his #20 ranking. Obviously, where inside that top 20 is very much open to debate. He's also the only guy near the top of this list who still has a lot of time to move up (or down).