In the NBA, on the other hand, you generally build laboriously, under salary cap rules that really hinder trading and free agency signings and through a draft that usually has a tremendous dropoff by the time you get to the already-decent teams. As a result, the best contending teams usually have a core of top-level talent that's also been together at least for a couple of years. So, when you do get to the playoffs, there's just too much of a gauntlet to run. Even the recent Bulls' and Lakers' dynasty had to flame out in the playoffs for a couple of years before breaking through.
From an organizational standpoint, starting on day one, the hardest league to win a title in is the NBA.
From other standpoints, like physically grueling playoffs, sure the NHL has some hard, hard working dudes.
But for gathering titles, the hardest one to fight to the top for is the NBA championship.