The best thing... Is both!
http://youtube.com/watch?v=SJgbUcx8MoU
That guy uses soul spear attacks and ghost spear attacks normally, fire imbue, but when he's in trouble, he switches to chains and ice imbue.
This is the ultimate strength character (Though it would be better if he was blade).
Whatever you do, DON'T be lightning!
If you don't do the dual imbue, I advise fire, easier on sp and stronger.