Here's the deal. The bottom line is this argument is simple. If you disagree with me, you're wrong.
Parise, to me, is a lock to be a good NHLer for a very long time. No doubt he will be a leader and an all around great player. He's just that type of player and has that attitude.
Vanek on the other hand is a little different. He isn't a lock to be successful, but he's certainly close to it. Vanek will never be a good defensive player and will probably not be the leader and all around player like Parise. However, offensively he has more potnetial. I've watched him many times this season, and this guy has an unbelievable touch around the net. He just knows what to do with it when he's there. Not to mention a great shot and great size. He scores big goals and is a force out on the power play.
What an earlier poster said is absolutely right. It all comes down to what you need. Buffalo lacks a true offensive sniper like Vanek could be, and he looks to be that guy. I don't know what NJ needs, but you can't possibly go wrong with Parise. Overall, I'd take Vanek. He has more potential and has a very good chance to turn out as a major goal scoring threat, which I feel he will be.