I'd guess shadow, but it doesn't really matter. Chaos, Shadow, and Life Steal don't have anything that specifically affects them. (Unlike Holy, which you can deal x2 on some opponents with)
The damage DOES ignore your AL, however, regardless of what it may be.
maybe this would be good in a ranger expertise/touch build?
Interesting idea... never thought of something like it... probably work better as for fun build thou... but then again... you never know.