BKH+5 is a great weapon for NG because most of it's damage comes from it's own base stats instead of from stat-scaling. If you rush to get it immediately with the Master Key, it makes the first 2/3 of the first playthrough extremely easy. However it's scaling is bad and it cannot be buffed so into NG+ runs and for PVP, it begins to fall off.
Pick a weapon that you like (because of moveset, style, whatever), upgrade it, get it's respective scaling stat/s to 40 and if you really want to push damage, pick up a weapon buff or use resins and then use power within to add damage. Personally I always liked Katanas paired with faith buffs in DS1 so in NG+ I'd run a Uchigatana +15 with Darkmoon Blade and Sunlight Blade depending on PVE/PVP and boss weakness/resistances.