Generally speaking, I cast Ice spikes, because it's an easy way to keep Paralyze on an enemy, without having to watch for it to wear off. However, when the fight really matters, I cast Shock spikes, to stun the enemy briefly when they hit me, and then just cast Paralyze on it, to get the best of both worlds.
Edited, Feb 5th 2008 2:32pm by Dragonli