to the best of my knowledge, damage-wise, it is indeed the solus greatsword.
it does 314 base damage and you can put another sharpening aug on it to make 324 base damage (personally i use a health aug because i tend to forget to block
)
the master greatsword is not as strong, even with 3 sharpening augs. it deals 214 base damage. 3 sharpening augs would make it 244 (i think sharpening augs add 10 damage anyway, seeing i put one on the frying pan and it added 10. perhaps its 10%, seeing the frying pan does 100 damage?).
im not sure of the damage augs add to the weapons base damage. is there a writeup about this anywhere?
in any case id pick the bereaver, just because it looks impossibly cool
reminds me of sub zeros kori blade from mk:da