The big difference with hockey is that a hot goalie can make a difference waaaaay out of proportion to the percentage of the players on the ice (one out of six at a time, or one out of 19 total, if you are shifting three lines of defensemen and four lines of forwards). If you look at the number of times that lower-seeded teams (five or below, assuming eight teams from each conference) make the Cup finals, you'll see the effect a hot goalie can have.
On the other hand, while great players can and often do have a tremendous effect on the outcome (one thinks of Michael Jordan or "Shaq & Kobe"), these players are usually on teams that were also top-tier teams during the regular season, showing the same level of personal dominance in leading their teams in all phases of play, as opposed to a specialty position like goalie.
So yes, to me it is fairly clear that the NBA playoff system is the one most likely to produce a champion that is a deserving team based on its regular season play, and thus the hardest to win.
The NFL is a clear second, and baseball (hot pitchers) and hockey (hot goalie) are much, much more likely to make the regular season meaningless.