there are a bunch of threads on this, but from what i have heard the difference is basically the stiffness difference of the pipe cleaner (alpha1) to ar6 (alpha2).
Next year, the Alpha 2 will be named the "Halo", Alpha 1 still called the Alpha 1. No change other than cosmetic from this year (Alpha 1 has a Pipe Cleaner core and base, Alpha 2/Halo has an AR6 core and base).
I have alpha 2s mounted at 2.5 back from center which is recommended. they ski great. they're not a true equal tip and tail ski so i wouldn't mount them centered.