The demon spear is a drop from the gargoyles in anor londo. And the lightning spear is good for a while, But it will eventually be outclassed. The dragon slayer's spear (ornstein's) scales with str and dex I think. But not that well (Cs on both?) plus I think it has kind of an odd move set that some people don't like. I personally haven't made it yet because I don't feel like putting points into str.