sonic blade lets you cover long distances and is easy to get the extra attacks. Arcanum is good for close quarters combat, but the arena is fairly large. If you want to get to seph before he casts sin harvest, i think sonic blade is the best tech to go with.
On the other hand, if you're up close and personal with seph you can deal tons of damage with arcanum. Though it's a lot harder to get the extra attacks.
On the other hand, if you're up close and personal with seph you can deal tons of damage with arcanum. Though it's a lot harder to get the extra attacks.