Sporting News ranked the 16 playoff coaches prior to the playoffs and Stevens finished 5th. Ahead of him where (in order) Pop, Carlisle, Kerr, and Doc.
I don't like Kerr being in the conversation. He's legitimately had the most talented team the last two years, and how much of it was due to his coaching is unknown.
It's really hard to do actual rankings, because it's hard to gauge how much impact each has had with the varying contexts. I think it should be in tiers:
Tier 1 Best Coach: Pop
Tier 2 Elite Coaches: Carlisle, Doc, Stevens, Budenholzer, Kerr, Stotts, Casey, Clifford, Van Gundy, Thibodeau
Tier 3: Good Coaches: Snyder, Lue, Malone, D'Antoni, Walton, Spoelstra, Kidd, Gentry, Donovan, Vogel, Brown, Joerger, Brooks
Tier 4: Average or First Time Coaches: Atkinson, McMillan, Hoiberg, Fizdale, Hornacek, Watson
I think Stevens is top-5 in the league, but he's certainly settled in the elite coaches category. There's actually quite a few really good/elite coaches in the NBA today constituting 1/3 of the league.