Ask a Bowman Thread.

I would personally go for blind if it was only between those two skills. Once time temple comes out, one pierce may not be enough to kill the entire row of monsters (and they don't stop to power up like skelegons do). You don't want to waste time using blizzard to avoid attacks. Also, the damage increase for leveling DB is very insignificant, as it doesn't gain anything other than tiny amounts of damage above level 21.