which one hits harder?

Titanium greatsword of fatal+10 80% or
Mithril Greatsword+10 40%

mithril greatsword +10 40% cdi. and oh! it also depends on how fast you hit :D

i think titanium 80% is better :) Well maybe titanium will be better if you got 50% Critical rate or above.

harder = better? Or harder to obtain?

Anyway the Titanium 80% is only good if you have a lot of rate otherwise you will deal low damage on the higher maps. Overall I would say the Mithril 40% is better in pvp and pve on higher maps because of the base attack.