Hmmmm good question. Both good boards and work well for different reasons. If you like boards with a single to double concave, swallow tails and want more of a hybrid ride and surf a bit flatter then go the Jacknife (Can still handle decent waves). The Hellrazor will surf a bit more vertical, handle good, bigger waves better than the JK, surf a bit more like a HP board.
Hope that helps or adds to the confusion :)