Hellbents suck for tree skiing unless you get them really short. (I ride old style 189s at 6ft and they are terrible in trees and tight stuff). They have a gigantic turn radius and are quite heavy. They are absolutely awesome when hitting cliffs, crud, and charging though.
The New Lifes are going to be much more nimble than Hellbents because they are way lighter and have a much smaller turn radius. They are a little bit easier to ski. I personally like New Lifes better, even though I have Hellbents. I've been planning on switching to something else for a while now. I just haven't chosen a ski yet.
Its really up to you. It depends on what you want more out of the ski. Hellbents are going to do better at dampening crud when charging fast due to their weight. But they'll be less nimble. The new Hellbents share the same attitude as the old ones. The extra width may be something you like, or not. I don't like it because it just makes them more sluggish and heavy, and I like lighter more playful pow skis. But everyone is different.
