From Basketball Prospectus:
4. 2008-09 Cleveland Cavaliers (10.0 rating | +8.9 regular-season differential | +11.1 adjusted playoff differential)
Because it ended in the Eastern Conference Finals, last year's Cavaliers team will be remembered by history as a disappointment. Still, from a purely statistical standpoint, Cleveland was a great team. The Cavaliers posted the second-best regular-season differential of the decade en route to winning 66 games, then rampaged through the first two rounds of the playoffs, sweeping overmatched Detroit and Atlanta teams. Then everything went wrong in the Eastern Conference Finals, but Cleveland was still barely outplayed by a very good Orlando team in a series that turned on matchups and poorly timed shooting slumps for the Cavaliers' guards. I'm willing to believe that, despite not reaching the NBA Finals, Cleveland was the best non-champion of the decade. Were the Cavaliers better than several champions? I'm not sure I agree with that.