I prefer the NHL playoffs for the most part, but there is no need to choose. The IIHF tournament is a different experience, held at different times and with, for the most part, a very different style. One plus for the IIHF tournament is that most fans by default have a team to support. I also somewhat enjoy the randomness of IIHF teams, where I really can't begin to guess which lines, pairings or even players a given team Canada will feature. I would rather see the best players, but there is a sort of enjoyment from seeing that Turris, McCann and Mantha randomly have good chemistry.
I do agree that best on best is missed. It doesn't necessarily translate to great hockey from an aesthetic perspective though. The 1996 World Cup and the 1998/2010 Olympics were extremely entertaining, for instance, while the 2004 World Cup and 2014 Olympics were pretty boring. The 1987 Canada Cup was also of course very entertaining, but that was when styles were very distinct. Also, when it comes to both the NHL and the IIHF world championship, the teams generally have more time together to gel and work on strategy than you see in best on best tournaments.