They both scale with different stats. The swordspear generally scales with dex but it can be hard to make a build for because of the faith and strength requirements. The greataxe generally scales with strength and has a bit of dex and faith scaling. Both are good for whatever you need them for but I'd generally say that the greataxe is more useful.

I have enough faith for both I was asking cause I want to have a main boss weapon, but if you have another to recommend i'm open to propositions