The chaos blade is probably my personal favorite. Its got great damage but also requires greater skill use because you loose some life with every swing.
My second favorite is probably the stone greatsword because it has good damage, a good moveset, and the Tranquil walk of peace R2 is pretty awesome in PVP.
Although my favorite character is still my Black iron build. Basicly hes a Darkmoon blade and strength build guy who uses the full black iron set, black knight shield/target shield, and a flaming greatsword (with stone greatsword backup).
Although my most played character is easily my Sunbro. He's a str/faith build that wears the paladin set, Solaire's shield, and uses the canvas talisman and stone greatsword/lightning claymore. Obviously being a sun bro I go somewhere, put down my sign, and just help people with their boss fights. Plus I get into some good PVP from time to time where my miracles mess up invaders
Another fun little build I play on occassion is my Darkwraith. Shes a level 8 character dressed in the wanderers hood, armor of thorns, guantlets of thorns, gold hemmed skirt, and uses the chaos blade and Dragon crest shield. With this character I invade mostly low level areas and before I mercilessly hunt down the master of that world I usually drop them a present like black knight weapons (also I run with unupgraded gear to make it more fair on invadees)
After I get my minimum level, base unupgraded gear, unupgraded weapon playthrough done Im going to be trying out a new Darkmoon faith build but focus on dexterity this time. I see this as a PVP character rocking the balder side sword/silver knight shield and wearing havels legs/gauntlets with some light chest and no head piece. I havnt worked out the details yet but I think he/she's going to be a fast roller with lots of miracles
Another build I want to do is one based around the dragon bone fist, thorn armor, and sorceries but theres literally no possible way to use the dark wood grain ring with that setup at soul level 120. So I dont know how well thats going to work out. Maybe I should just start a soul level 200 PVP league?