Recently replaced my Hogg It and had a similar dilemma. I personally went w/ the Sword... but I've only compared it to the Extreme.. haven't seen a Viper in person yet. The durability of the fibers was one of my big determining factors in choosing the Sword over the extreme.Tough choice.
I think the Sword would be brighter, and the light comes with it, if that matters.
I know thier fiber optics are vitually unbreakable also