Well, I know you only want to discuss these 4, but in my mind they are still all behind Ryan Murray. Murray is also draft eligible in 2012, but is just shy of the 2011 draft due to his Sept. birthday.
But if we are only looking at these 4, here are my thoughts.
1. Griffin Reinhart - He is the best of the 4 named in my opinion. He is big at 6'4. He plays with a mean edge. Loves to play physical and throw around his big frame. Has a good hard shot. A strong passer as well. Definitely has the offensive side of his game as well as being very good and mature defensively. Despite his size his skating really isn't an issue.
As far as potential I think he is at worst a top 4 defender on an NHL team. I think he has enough to be a top pairing player that plays top unit PK and maybe second unit PP.
NHL comparison: I want to say in a Pronger mold, but I don't want people to think that I think he is going to be the next Pronger, which he obviously won't be. But think along those lines and that's what you get from Reinhart.
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2. Matt Dumba - To me it's a toss up between him and Pouliot for second on this list. Dumba is just an explosive player from the blueline. He hits like an absolute truck. He has a bomb of a shot and is a great skater and passer. He is definitely the most explosive out of the 4 players listed in the thread. He is also the most raw though. Still is considered rough around the edges, but if he can ever add some polish to parts of his game he could easily end up as the best of the 4.
I think his potential is a top 4 defender who plays both PP and PK.
NHL comparison: A righthanded Dion Phaneuf. I also think PK Subban is a pretty fair comparison.
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3. Derrick Pouliot - I have to say I wasn't overly impressed with him the one time I saw him live this season. But, that was obviously a very small sample size. This ranking is based more on past performances and doing some reading on him. A very smart and effective 2 way defenseman. Most famous for his skating ability as it is already near an elite level for a defenseman. I think he is probably the best offensive defenseman out of the 4, with Rielly a close 2nd.
Potential is a top pairing defenseman who can QB a PP and likely see time as a 2nd pairing PK guy.
NHL comparison: Duncan Keith
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4. Morgan Rielly - It's really mindboggling that this guy can be 4th on the list because he is an amazing player. As far as blazing speed and game breaking ability, Rielly is likely the best out of the 4. He isn't as pure of a skater as Pouliot but he is faster and likes to lead the rush just as much, if not more. He's got great passing abilities. He's not an overly physical defender but is very SMART in his own zone. Reads the play well and has a quick stick to make up for that lack of physicality.
For potential I say he will likely end up as a top 4 defender who will play on a top unit of a PP and may or may not kill penalties.
NHL comparison: John-Michael Liles (almost to a tee)