My build is as is follows:

5/5 Aimed
4/5 Nox (no last update)
2/5 Pierce (I like the health upgrade too)
4/5 Veil (no explode)
5/5 Dex, Str, Int, Crit, Armor

I tried traps, but can't seem to be able to master them. Plus, I run Arena a lot and veil is definitely more useful there than traps. I don't like razor, I'd rather have some more armor for the time being.

As for the 3 targets upgrade on pierce, just consider this: You are trying to avoid a boss red zone and there is one mob around. That upgrade will hit boss, hit mob, and then bring you back to boss for a certain death.