I've really fallen in love with this particular setup that I mashed together over the last few days. This build was designed in v. 1.06 and designed to PvP both in Lordran in general and for Arena pvp. With my (mediocre) pvp skills, this was able to net me an 85%+ win rate, highest streak being 15 kills in a row, in one sitting. No parrying skill or backstab knowledge needed, although it helps.
This class isn't set in stone. Once you get the most important bits (min requirements for equipment and miracles needed), the rest is up to individual preference really.
Starting class: Bandit
Vit: ~30. How much you need is dependent on your play style, how well you manage your endurance, and how much damage output you would sacrifice for more durability. Between 20 and 40 recommended. Personally have 29.
Attunement: 12 (two slots).
Endurance: At least 32 (more on this later). Personally have 34.
Strength: 14 (min. requirement for Great Scythe)
Dexterity: 30-40 (scaling for Great Scythe). Personally have 40.
Resistance: 11 (base)
Int: 8 (base)
Faith: at least 30, at most 40. Personally have 35.
Right-hand weapons: Great Scythe. Suggested: a Katana type or Rapier type is good for changing up the game, Black Bow of Pharis for ranged harrass, Lifehunt Scythe if the opponent is shield turtling/already used up weapon buffs.
Left-hand weapons: Grass Crest Shield for stamina regen and the fact that you won't be using a shield for blocking very much anyway. Canvas Talisman (unless you are 40 faith, in which case use Darkmoon). Blood Shield if using the Lifehunt Scythe to counteract the self-inflicted bleed buildup.
Rings: Ring of Favor and Protection. Havel's Ring/Wolf Ring/Red Tearstone Ring/Cloranthy Ring depending on the situation.
Armor: Any armor that brings you to just below 50% weight, or 25% if you must have that fast roll. Fast roll is overrated IMO. My favorite combo (though by no means perfect) is full Catarina sans leggings, Guardian Leggings for below 50%, or Mask of the Father/Catarina Chest/Catarina Leggings/Havel's Ring/Elite Knight Gauntlets instead if speed is a priority.
Darkmoon Blade or Sunlight Blade. Darkmoon Blade is preferred due to higher damage, but Sunlight Blade doesn't require membership of the Blade of the Darkmoon. Plus, it looks cooler, and isn't shut down by Great Magic Barrier like Darkmoon Blade does (since it deals lightning damage instead).
Great Magic Barrier/Force/Great Fireball/Any non-sorcery spell to your liking here. Great Magic Barrier is a godsend against WotG spammers and spell builds (esp. useful with the obsession of Pursuers and Dark Bead these days), while Force is a great time-buyer should you catch yourself with your back open (a common occurence when using the Great Scythe).
Great Scythe/Lifehunt Scythe
Your key element is sheer damage output and surprise. People don't seem to realize how much damage the Great Scythe is capable of in the craze of using super slow str weapons such as the Black Knight Greataxe or super fast dex weapons such as the katanas and curved swords. Use this to your advantage.
The Great Scythe is a weapon with a lopsided moveset. In general, anything that involves light attacks really, really sucks, while everything that involves heavy attacks are really, really good. The light attacks are all vertical, very slow for R1 attacks, have terrible hitboxes, and track horribly with strafing opponents, while the heavy attacks deal massive damage, and have horizontal, sweeping hitboxes. Always two-hand the Great Scythe unless you are going for a parry because any time you are raising your shield should be used to get away from the opponent instead. Stamina usage on the weapon is crazy and trying to block after combos will likely get you staggered.
The combo to use with the Great Scythe is to use the running attack, followed by two R2 attacks. This allows the player to do an almost 360 degree sweep around him/her, almost always hitting an unaware opponent. You'll need at least 32 endurance and the Ring of Favor and Protection to pull this off. With 40 dex, 31 Faith, and Darkmoon Blade, I was pulling off 600-1000 damage PER HIT. This kind of raw power kills most enemies at level 100 if two or more hits connect. Even if it doesn't, the enemy will usually get freaked out by the display (or the fact that one or two hits took down half his/her HP), allowing you to back off and recharge your stamina.
The jump attack is good, with good range, an excellent hitbox, and low starting and ending lag. Use it to punish people trying to parry you.
The Lifehunt Scythe is very similar to the Great Scythe, possessing an identical moveset. The fact that the Lifehunt Scythe requires 16 strength to one-hand is meaningless since you should always two-hand the scythe weapons anyway in my opinion. It deals slightly higher base damage than the Great Scythe at the cost of shorter reach. It's also slightly heavier; take care to readjust your equipment when you use it to not get the slow roll. Last but not least, it has insane bleed buildup and bleed damage, which is great against shield turtlers.
Unfortunately, the Great Scythe and Lifehunt Scythe do have their weaknesses. This is the reason why I call this build the "Boss" build: You will appear intimidating and tough to an opponent at first glance, but once they find your weaknesses, they can exploit it and kill you if you don't finish them off quickly. In particular, using the combo I prescribe will leave you wide open to retaliation attacks if the opponent calls your bluff and doesn't back off once your combo is finished. The all-in offense nature of this playstyle and the poor rolling attack option exposes users to powerful ranged sorceries such as Dark Bead (countered easily by Great Magic Barrier, though). The Great Scythe's flailing motions leave you open to backstabs for people who can precisely time your movements in sync with theirs. Spear turtlers are hard to deal with as even if you manage to hit them with all three hits and get them to stagger, your high stamina per swing makes it hard for you to capitalize on that. Bleed buildup can help against these guys, but since all you need to do to avoid bleed is roll when the build-up, it's not a guarantee. The Great Scythe is terrible at staggering opponents with its swing speed and stamina consumption, so many opponents can out-poise you in a button-mashing contest. Use Force (or Wrath of the Gods if you're an asshole) to buy yourself time to recharge.
Once you're sure that your opponent has got your Scythe combos figured out (if he/she is even still alive by that point), it's time to switch up your arsenal.
The ultimates weapon of balance, katanas are a blend of speed, damage, reach, and stamina economy. They're excellent standard weapons to fall back on, if nothing remarkable. As an added bonuses, they also cause bleed, stacking with the Great Scythe. I personally use Iaito for the useful R2, but the Chaos Blade might be a better choice for higher damage output (and the fact it can't be buffed is a moot point since ideally you've used that buff on the Great Scythe already). Since both the Lifehunt Scythe and the Chaos Blade require 16 strength to wield with one hand, it might be beneficial to drop two more points into strength if looking to use this combo (unless you're content with always two-handing weapons).
The shotel is this build's only effective counter against careful spear turtlers. Equip the Wolf's Ring and some heavier armor before taking them on, and use Green Blossoms and the Grass Crest shield so that you regenerate stamina more quickly than them.
Rapiers are a foil (pardon the pun) to the Great Scythe. Whereas the Great Scythe is a run n' gun style, rapier users are cautious. Whereas the Great Scythe focuses on wide attacks with dead-angling and throwing players off with aggressiveness, rapiers focus on precise game mechanic manipulation for backstabs and ripostes. I like to think that switching to a rapier type is akin to changing a stance in swordplay to confuse your opponent, but how well this works depends on your opponent. The Estoc (for its reach) or Ricard's Rapier (for its R2 against sluggish opponents) are the prime candidates here.
I'm still faintly dazzled by the extremely high success rates I've had with this build so far. Take a shot. I promise it's not disappointing.