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What about a Bowie knife with a jagged blade? Brutal seems like a good property to represent the extra ripping and tearing, and it's certainly not a heavy blade...
Both superior. So, taking kukri over the rapier gives you 0.5 less average damage, costs +1 to hit, and gains you the ability to use in your off-hand. Obviously, the only reason to use a kukri in that analysis is to have it in your off-hand. Otherwise, the rapier is strictly better. At large size, the kukri is 1d8 brutal 1 (average 5) and the rapier is 1d10 (average 5.5), so that doesn't change with the large versions.
Brutal weapons really do nothing to improve your power; they just reduce the fluctuation of damage. Which is good, but really... not what one should be worried about IMO...