Golden State is #1.
I think the Rockets are #2.
The Celts are winning with defense and clutch plays. I'm not sure how sustainable it is, but they're clearly still one of the best teams in the East. I'm not sure how they're managing to be so coordinated on both ends of the floor after so much turnover and such a young roster. It's incredible. Brad Stevens is the runaway Coach of the Year candidate so far.
After that, it's hard to say exactly. The other "good" teams have been very up and down.
I don't believe in the Pistons, I don't think the Raptors are better than they've been in the past, and I'm not surprised the Thunder are struggling. I'm kind of happy they are, actually, because I hate the way they play. I don't believe in the Magic.
I think the Spurs will be in the mix once Kawhi comes back.
I might actually say the Blazers are the 5th team, considering they're top 5 in defensive efficiency with a significant point differential and two elite scoring guards. I don't think they will be all season, but the Lillard - CJ - Nurkic trio seems legit.