I think it’s clear who the top three are:
Popovich
Stevens
Spoelstra
In that order. I was never the biggest fan of Spo but now I’m convinced, he’s legit.
As for the fourth? I’ve been impressed with McMillan the most, and he’s been around awhile. Sorry but D’Antoni (we’ve seen this rodeo before, we know how it ends) and Kerr (anyone can coach that group, even Luke Walton and MIKE freaking BROWN!!) don't impress me much.