There is no best weapon. Each weapon has its own little use, and its cost fluctuates accordingly. Eternity, for example, can prevent deckouts and can be used as CC, but it's expensive. Vampire Stilleto, on the other hand, makes a life swing of 8 every turn, which isn't spectacular, but it's cheap. Trident, however, is probably the most use-impaired weapon. (it is semi-expensive, to boot)