Depends what you mean by best. Many of Nomura's designs are amazing just because of how impractical they'd actually be outside of a fantasy setting.
Caius takes the cake in the "biggest sword" villain dickwagglin contest. If Sephiroth had been using that sword, forget a simply dead Aeris, there'd be Aeris kibbles all over the room.
I assume this contest doesn't include Chaos?
cuz I mean: