I would like to rank NBA teams in each season by some sort of metric, and I'm not sure if something like this exists already or not. It would be better if it was a metric that can tell me how good an NBA team is before the start of the season.
A very easy, and direct way to rank the NBA teams, is by their record. So a team that has won for example 50 games in the season, and lost 32 (a total of 82 games in the season), would have a 50-32 record, as they call it. This team, even if in a difference conference, would be better than a team with let's say, a 40-42 record.
Firstly, however, the above method only takes into account the regular season, and doesn't mention anything about the post season (i.e, the playoffs). Therefore, if for example both the 50-32 and the 40-42 teams do make it to the playoffs, and the latter beats the former, then obviously the 40-42 should be ranked higher than the 50-32, even if they had a lower winning percentage than them during the regular season.
Another thing to keep in mind is that there is a difference, albeit slight, between the two conferences (the East and West), especially this year. The West, based on winning percentages of the teams, was considerably stronger than the East for this season's NBA. Therefore, it might be something to take into account because Eastern conference teams play each other more often than they play Western division teams for example. Some might say then that the Indiana Pacers or Miami Heat for example, who ranked 1 and 2 respectively in the regular season, might have had an "easier schedule" than the San Antonio Spurs who finished first in the Western conference, even as they had a better winning percentage.
All in all, winning percentages (i.e a teams' record) usually is what determines a teams rank overall in the NBA, but something that might be taken account, as mentioned, is how far a team advances into the playoffs, or which conference it stands in.
FiveThirtyEight uses Elo and CARMELO metrics to rank NBA teams before the start of each season and during the season. Elo is "a simple measure of strength based on game-by-game results." CARMELO is FiveThirtyEight's "Career-Arc Regression Model Estimator with Local Optimization".
Here are their rankings prior to the start of the 2018-2019 NBA Season (choosing the forecast from Oct. 15, the earliest available projections).
- Warriors (1685)
- Rockets (1654)
- Jazz (1623)
- Warriors (1751)
- Rockets (1662)
- Raptors (1655)
Elo is most likely more accessible than CARMELO, so that is one way you can rank NBA teams beyond a given team's record.
Basketball, like many other sports (e.g. Baseball) is starting to lean toward statistical analysis to judge efficiency and overall success from not just an individual players standpoint but also from a lineup and team performance basis.
Former ESPN analyst and current front office personnel man for the Memphis Grizzlies Greg Hollinger created a power ranking system (which can still be seen via espn.com, although you might need an paid insider pass to gain access) in which scoring margin (or average margin of victory) plays a heavy role in determining which team is better than the other.
While this is not an official science, Mr. Hollinger's rankings are commonly accepted by a lot of his former analyst counterparts.