They're all good
. Well, not necessarily equally so depending on circumstances... blood magic may be tricky if you can't sacrifice the gold income, or you're the Ashen Empire and can't find people left to sacrifice...
Quickness comes from Alteration, Blood is a very fine summoning school (and Astral Corruption will be welcomed with open arms by your fellow players), Enchantment provides a lot of globals as well as the most feasible way to get rid of them... etc.
Real nastiness can result from combinations. For instance, Wind Guide + Flaming Arrows, for instance. Curse of Stones + Relief. Quickness + Communion + Orb Lightning...