The NHL's current (that is, pre-Covid) playoff format is the best in sports.
1) You have to be a pretty good team to make it to the playoffs but enough teams do get in to keep the regular season interesting. Upsets are possible in every round but you've gotta earn it by winning 4 out of 7.
2) Four 7-game series is extremely challenging, so it's very hard, if not damn-near impossible, for a mediocre team to back into a championship.
3) The 4 x 7-game format is simple, straightforward, and easy to follow and understand (no byes, no having a different number of games in each round, and it's the same every year).
(The only issue I have is the way they currently determine how teams qualify and seeding/matchups. But I would strongly oppose abandoning the 4 x 7-game series structure in favour of some gimmick format.)