A unique skill that 1st round pick Marek Vanacker has - he is unusually adept at dislodging and/or stealing the puck from whomever he is defending. There may not be another prospect quite as good at this as Vanacker is. Regarding A. J. Spellacy, he is bigger than you think - 6' 3" and just over 200 lbs. He is an exceptional athlete and received five scholarship offers from NCAA Division i-A football programs, playing both safety and wide receiver. He is a physical player with both excellent foot speed and athleticism.
You guys are sleeping on Ethan Del Mastro, didn't even mention him. He was an AHL Allstar in his pro rookie season. 6'4" 210. Decent skater. Super smart shut down defenseman that has decent offensive ability.
My pick for underrated prospect, FWIW, is Roman Kantserov. The only criticism on him is he is slightly undersized at 5' 9" but he is very solid and muscular at 175-180 lbs. He is an excellent skater, has a high hockey IQ and sees the ice well. He also has very quick hands and a wicked shot.
