There are many different ways to measure “best”, but NBA Stats has one simple metric called net rating. Net rating is point differential (i.e. points scored – points conceded) per 100 possessions. Here are the ten active lineups, that played at least 360 minutes (not a large sample, but not a small sample either), that had the highest net ratings. (Data from here)

1. Duncan, Green, Leonard, Parker, Splitter (SAS) — Net Rating; 18.1

2. Allen, Conley, Gasol, Prince, Randolph (MEM) — Net Rating: 13.4

3. Durant, Ibaka, Perkins, Sefolosha, Westbrook (OKC) — Net Rating: 12.3

4. George, Hibbert, Hill, Stephenson, West (IND) — Net Rating: 12.1

5. Bosh, Chalmers, Haslem, James, Wade (MIA) — Net Rating: 11.9

6. Butler, Green, Griffin, Jordan, Paul (LAC) — Net Rating: 8.5

7. Ellis, Ilyasova, Jennings, Mbah a Moute, Sanders (MIL) — Net Rating: 6.7

8. Faried, Gallinari, Iguodala, Koufos, Lawson (DEN) — Net Rating: 6.5

9. Allen, Holiday, Richardson, Turner, Young (PHI) — Net Rating: 6.0

10. Curry, Jack, Landry, Lee, Thompson (GSW) — Net Rating: 5.7