Personaly (but what do I know, Not very much)
I say Impulse just cause I have one.
(although I used a shocker the other week and they are both sweet,)
What position do you play. I found that the shocker was great at the back, accurate, quick but when i broke up front it was big and heavy but I was not used to it.
My Impulse I can use left handed and could have done some better moves than was done with the shocker.
The Impulse has the advantage of being able to pull out the bolt easily on the field if you need a good clean out I don't know how much work goes into the shocker but from what I could see it was quite hard to do.
Hope this helps