Which weapon should i use my somber ancient dragon stone on?

I’m on my first play through, looking to try out a new build or weapon since i’ve been using blasphemous blade for quite a while now although it’s still not +10, so i was wondering if i should either use my somber ancient dragon stone on that, on the bloodhounds fang which i haven’t used in a while but is already +9 or for my rivers of blood which i have upgraded with the tons of spare stones i had but haven’t actually had to chance to try it out or upgrade it all the way to +10. What do you guys think? I’m at the fire giant right now (which is causing me a lot of trouble) so just wanted to switch things up a bit.