I think Morin has the highest upside which is a 6'7" (possibly still growing) 220lbs+ two way #1 Defenseman with massive strength and a meanstreak to match his skill.
I also think highly of Sanheim, because I believe his ceiling is a 6'4" 220lbs two way #1 defenseman. However, in place of a meanstreak and punishing checking skills, he has awesome offensive vision and creativity.
Ghostisbehere is an awesome prospect as well and was playing like a superstar in the Frozen Four. He also has the potential to be a 5'11" two way #1 defenseman with great speed and playmaking abilities.
As you can see, I think we have three great defenseman in our system and I think they all have incredible potential and they're all players who "step up when it matters most" and have all been on the upward trend. Basically I would just have to rank them by sheer ability to impose their force on the game. Morin has that ability in spades. Being so huge and nimble while also being strong and precise is a great package to have in a #1 dman.
Laughton is a great prospect too, but I think he's the prospect closest to making the team and I also think his potential may be limited due to two incredible NHL players in Claude Giroux and Sean Couturier. So unless one of those three play wing in the future, Laughton's highest upside is still going to be a superb 3rd line center. However, this is not a bad thing at all. Center depth is as important as defensive depth in winning a championship, Laughton's future is like a potentially higher scoring Jarret Stoll.
1. Morin
2. Sanheim
3. Ghostisbehere
4. Laughton
5. Hagg