Personally, I have a strong bias toward the original Slammer. It's just hard to put down a bait when you have so much history with it, especially the individual 'money' baits that you know get bit.

I do throw the X-2 sometimes when I want to fish very slowly on top. Just barely turning the handle with the X-2 will still get you a squeaky slow wobble and I dig on that :)

Someone will probably post now and say they like the X-2 for burning the bait but that's just my personal thought on it. It's hard to really fish a Slammer wrong and I've caught fish on the same baits doing anything from deadsticking, to barely turning the handle, to moderate retrieve, to super fast subsurface retrieve. It's a "fish mood" thing a lot of times and it never hurts to mix it up during the day if things are slow.