I'm about to embark on an exciting project that will attempt to answer who are the best coaches in the league. It'll involve a lot of data, so it will probably take a few weeks. But I'm super excited.
My observation, admittedly without any effort or analysis whatsoever, has been that there are usually 2-3 really good coaches in the league at any time who are able to move the needle in a positive direction just by virtue of being with a team. Trotz is the big example that comes to mind currently. Gallant is getting there. Darryl Sutter always had his Kings teams punching well above their weight class.
Otherwise I think the difference between the rest are more or less negligible. I mean, looking back at the list of Jack Adams winners you see guys like Bob Hartley, Patrick Roy, Doug Maclean, Dan Bylsma etc. While the NHL awards are not definitive it's always seemed to me like hockey coaches more than any other sport are the cream of the crop one year and out of a job the next. I remember people on these boards were absolutely swooning over Bylsma when Pitt was winning and after the HBO special like he was Scotty Bowman and now he's the AC for the Wings.
Interested to see what you come up with.