Arsenic is cool for a... dunno... badass spacecraft, but it is far from being the coolest weapon IMO.
I like lobotomizer the most, it's like a freakin POW! hammer-sword directly into your brain! And the name just adds to the coolness.
Farenheit is cool too.
the ones I dislike the most are Titan (I mean, come on, seriously?) and Eternity (Doesn't look like a weapon at all).