fast casting or soul reaping?

what's more useful? fast casting or soul reaping?
(my gut reaction says soul reaping for PvE and fast casting for PvP but i'd like a few opinions on it for teamplay)

I say trust your gut.

Are you a PvE Death Necro?

If so, then Soul Reaping is worthwhile. Otherwise, avoid it.

Peace,
-CxE

Here's my ranking of primary attributes:
1. Expertise
2. Energy Storage
3. Divine Favor
4. Fast Casting
5. Strength
6. Soul Reaping

if you are not going to touch any long cast time spells... then you wont need fast cast... and I dont consider most of the necro spell long... nor the mesemer... unless you are going to race someone to a certain spell.