I have heard nothing but problems with the livewire. And have heard some kinks are still being worked out with the xcal3, I am unaware of a benefit to the xcal3 but i could wrong there. I bought the xcal2 recently just cuase it was time tested and battle proven. I dont know anything about the predators but more people seem to use the xcal.
The Xcal 3 is almost the same thing as the xcal 2. I believe the xcal3 does have more memory. As far as the livewire goes. You'll need to add some extra stuff in order to make it full functionally. I remember something like welding a bung to get a proper a/f etc...
The Xcal3 is a lot more similar to the livewire than the Xcal2. The livewire and Xcal3 issues have been pretty much worked out. To get proper AF using the livewire you will need to weld in the bung as well as buy a wideband. I have great deals on all this stuff.
i have the livewire and its pretty good, some stuff are inaccurate like the hp/tq numbers and i believe they are waiting for the firmware. the livewire can do more, so if you dont mind spending an extra 200, its worth it.