If you want to know which weapon is better currently, i say: Hyperconductive Nothung.
It allows you to save Lore to buy armor, while spending 1k of those may hurt your armor iLvl.
Despite the fact Lore weapon has 2 materia slots, i believe it's not worth to exchange those for perfect secondary stats (at least for me but i play aggresively) that Nothung provides with.
BUT, if you speak about future, like next patch, or next expansion, i would say: Hellfire- if you have specified standards about statistics for DRK arm.
Since current relic posses CRIT & DET as stats, i doubt next relic is gonna have same sweet stats. That means you may end up making relic with parry and accuracy.
(While i have nothing to parry, for current moment it is not a too good statistic)
Next relic may also be a hybrid of crit/det & parry/acc, but it is still less interesting than current Nothung stats.
It may end up, that grinding next tomestones or weapon available will be a better choice than a relic.