I think a lot of folks are making lists based on how these players were in previous seasons. Or just pure reputation. I'm trying to rank them mostly on this playoffs.
Neither Bouchard or Heiskanen had a great regular season. And Heiskanen is now just coming off of his injury, so perhaps that's why he hasn't had a special showing. But clearly all the folks ranking Heiskanen ahead of Bouchard are doing it based on what they've seen from Heiskanen in previous seasons right? Because Bouchard is the more impactful player right now. Bouchard has set a very very high bar with his postseason play.
Bouchard
Heiskanen (Ekholm might be around this level if healthy)
Harley
Walman
Kulak
Lindell
Klingberg
Nurse
Bichsel
Ceci
Lyubushkin
It's a bit hard to tell with Dallas' defenders because they have several guys - Lindell, Ceci, and Lyubushkin, all getting hard defensive minutes, and all getting solidly outscored. They aren't succeeding, but it's a tough challenge. So I'm partially ranking them based on previous play. Otherwise LIndell might be even lower. Bichsel has better results but gets easier deployment. He'll be a great player but you can still see him bobbling a lot of pucks under pressure.
Kulak is perhaps the most underrated. Yes he's struggled at times in top 4 roles in previous seasons but he's playing really hard minutes in this playoffs, big minutes and usually defensively skewed, and crushing at it. Rangy defender and his escape speed is a problem for forecheckers.