Drake Sword, first time through I didn't understand the scoffing either. I thought I was invincible, end game gear, bosses will drop like butter.
Then I hit the wall that is Sen's Fortress. Back at square one with no upgraded weapon. Lighting Spear transition is just ok, but doesn't pack a huge punch in Anor Londo either.
So I was screwed until I could level up or convert a weapon. I had been leveling up Vit and End to no end, but not gear. Total wrong way of doing it in retrospect IMO.
Now, after 4 playthroughs of one character and starting a new one from scratch, leveing gear first and foremost, then stats.
In the depths right now, already have a Uchi +10, and the pyro glove at +15, yeah baby. Slimes take only 1 combustion, drop shards pretty regularly, you can level up stuff super fast here.
Almost everyone I helped on the Gaping dragon the past few days was using the Drake Sword. Wanted to msg them saying ditch that crutch post haste, but they'll figure it out.