Dragon Thrust or Critical Magic?

Slow is really useless.

Hardly. Works amazing at Kents, Wyverns, and eventually gallops and ToT, and is much better then Thrust, I haven't used thrust since 80, and that was to confirm if it worked on Bosses or not. Slow has saved my ass many times when my skills failed to Freeze/Stun a monster. It is useless when you 2hit/1hit everything though, along with Thrust. I find thrust to be quite useless as you'll be hitting anything you stand on anyways.