Well, out of MK4/Gold, I'd say the best weapon was Sub-Zero's ice lance dealie because being able to freeze anyone with it, regardless of who you were playing as, was pretty cool.
In MKDA, I'd say I liked Kitana's fans the best, mainly because it was Kitana and she had a cool impale move with the fans.
In Deception, I dunno, I'd probably say Jade's staff because of how much damage it does.
As for the worst, I have no idea, I've never really thought about it. Overall the weapons in MKDA and MKD were pretty boring since so many people had a certain type of sword that didn't even look that different from the others.