JKSManga
the demon form consciousness my guess would be that it is Quinns deepest darkest traits his love of fighting, completely overwhelming and destroying the fighting spirit of his opponent, and of course as someone else said in another comment complete lack of morality and attachment and thought of what those he loves will think of his actions
Well Vampire demon form is much better than bloodsucker form, since it is evolved form of bloodsucker. Bloodsucker form does have lot of restrictions like can't use blood power or shadow ability and only advantage is it double all stats than normal, But Vampire demon form can use blood, shadow and I think it also double stats and even more, though when used Quinn goes on rampage.