I'm surprised John Hollinger's Player Efficiency Rating hasn't been mentioned in this thread.
I'm a big analytics guy and tend to focus on PER and Win Shares.
Only 20 times in NBA history has a player posted a PER above 30 (doubling the efficiency rating of the average player) for a full season. Four players have accomplished that feat multiple times: MJ (4), Lebron (4), Wilt (3) and Shaq (3).
Here's the full list:
1. Wilt Chamberlain (1963) - 31.82
2. Wilt Chamberlain (1962) - 31.74
3. Michael Jordan (1988) - 31.71
4. Lebron James (2009) - 31.67
5. Michael Jordan (1991) - 31.63
5. Wilt Chamberlain (1964) - 31.63
7. Lebron James (2013) - 31.62
8. Stephen Curry (2016) - 31.5
9. Michael Jordan (1990) - 31.18
10. Michael Jordan (1989) - 31.14
11. Lebron James (2010) - 31.11
12. Anthony Davis (2015) - 30.8
13. Lebron James (2012) - 30.74
14. David Robinson (1994) - 30.66
15. Shaquille O'Neal (2000) - 30.65
16. Shaquille O'Neal (1999) - 30.55
17. Dwyane Wade (2009) - 30.36
18. Tracy McGrady (2003) - 30.27
19. Shaquille O'Neal (2001) - 30.23
20. Chris Paul (2009) - 30.0
Note that no one accomplished a PER over 30 between 1964 and 1988 until Jordan did it...and he did it four straight seasons.
Only five players in NBA history have accomplished a Win Share of 20 or more: Wilt (6), MJ (3), Kareem (3), Lebron (1) and David Robinson (1).
1. Kareem Abdul-Jabbar (1972) - 25.4
2. Wilt Chamberlain (1964) - 25.0
3. Wilt Chamberlain (1962) - 23.1
4. Kareem Abdul-Jabbar (1971) - 22.3
5. Wilt Chamberlain (1967) - 21.9
6. Kareem Abdul-Jabbar (1973) - 21.9
7. Wilt Chamberlain (1966) - 21.4
8. Michael Jordan (1988) - 21.2
9. Wilt Chamberlain (1963) - 20.9
10. Wilt Chamberlain (1968) - 20.4
11. Michael Jordan (1996) - 20.4
12. Michael Jordan (1991) - 20.3
13. Lebron James (2009) - 20.3
14. David Robinson (1994) - 20.0
And only four players have had a season with a PER of 30+ and a Win Share of 20+.
Wilt Chamberlain (3)
Michael Jordan (2)
David Robinson (1)
Lebron James (1)
I'm not sure about my Top 5 but imo Jordan is the greatest ever, Wilt is likely second just based on his dominance over the inferior competition at the time he played (sort of like Babe Ruth) and Lebron has already accomplished enough in his career to warrant a spot in the Top 5 at least.
Underrated players who I don't think get enough mentions in 'All-Time' discussions like these: Shaq, Oscar Robertson, David Robinson, Karl Malone, and Dirk Nowitzki.
Overrated: Bill Russell