I've been playing Darius frequently since his release, and have tried multiple types of builds for him, some which worked, some which didn't and some that worked better. After a day and a half of playing him, I found the build which in my opinion worked best.

First let me explain my impressions of Darius. He is Garen's evil/more offensive twin, so much so that Riot felt the need to include a mockery of Garen's spin attack as Darius's Shift-1 joke. He can spin like Garen and has an ultimate that is very much also like Garen's. So I decided to build him as I would Garen but with slight alterations. The result was an extremely offensive champion who had the endurance to wade into battle and get multiple ultimates off and walk away alive.

Attack Speed Darius - Many players have tried going this route due to Darius' Passive skill, to sooner apply all 5 stacks of his DoT. I find this unnecessary as his abilities also trigger this bleed out, allowing a full skill rotation along with an auto attack to already apply 3 stacks within 1 second. The bleed out also ticks off at a predetermined interval, not after every hit like Varus. Attack speed is not needed because you have additional DPS hitting with your bleed between hits and extremely low cooldowns. This build can still be effective in 1v1 scenario's but in a team fight, people will know to target you, and with no escape mechanism, you are dead.

Tank Darius - Not going to go too deep into this. Darius gets amazing attack damage returns, his Passive bleed used .4 of all bonus AD, his Q .7, his W 200% all AD, and ulti .75 and 100% true damage. It's a waste of the champions damage output and other champions fill this position better with their skill set.

The runes are a standard bruiser build. I don't go insane with armor pen due to Darius' built in passive, but I allow for just enough to give him a free Last Whisper.

The Masteries are also a standard choice, I don't feel the need to explain them due to the fact hundreds of other guides must.

If I am truly soloing top 1v1 I go boots, but if it is me against 2 players I grab cloth armour and five potions to avoid being bullied out of lane and park myself near turret.

The Triple Doran's Blades may seem excessive, but they're not. They give you 240 additional health, 30 damage and 9% life steal. They are intended to fill item slots and give you the damage and health needed till Atmog's is finished and you can continue building hard damage.

Brutalizer is also intended to fill this goal, its 25 damage, cooldown reduction and extra armor pen help you keep slicing through even the hard tanks till late game when you've maxed your E.

I finish my boots at this time, I usually go Merc Treads, but not always. If the enemy team doesn't have a whole lot of Crowd Control, or heavy AP damage I may go Ninja Tabi.

I start Warmogs with Giants belt as I have 1 slot still open, and couldn't care less about the 200 health or slight health regen boost the other items give me.

After Warmogs is finished I start Atma's with the Chain mail, This item combo gives me an addition 900 health (with the potention for 600 more) 45 armor, additional crit chance, and turns my max health into 55-60 additional damage. All the while making myself harder to kill while snowballing in damage.

I take this time to finish Youmuu's Ghostblade after Atma's is complete. Ghost blade allows for better pursuit of fleeing enemies and extra dps after my abilities are on cool down.

I then start making Blood Thirster. This item makes me even deadlier while still synergizing with the survivability of the build

Gaurdian Angel is the Default Item I choose for a balanced team 1-2 AP champs 3 AD champs. Any more AP damage than that and I opt out of Maw of Mal (for additional Magic resist, a barrier and extra damage). If its a heavy AD team, I will go Flaming cloak for more health, more armor, and additional dps. If we have no REAL tank, I will grab thorn mail.

Q takes priority of the three basic abilities due to its low cooldown and heavy damage (150% if you clip them on the outside of your AoE) This is both your poke and your bread and butter skill.

W follows up in priority due to its slow and lvl 5 dealing 200% weapon damage, its cool down lowers a second for each stack of bleed you have on a champ (max 5 seconds). You do not max this skill first because at low levels will a low maximum attack damage total, your Q does more damage and has more range.

E comes last as it is primarily a utility skill and if you're playing right, has a longer cool down than your ult most of the time. I grab one at lvl 4 and ignore it till I can't level anything else. You can use this ability to pull enemies out (and into) turrets, and secure a kill when they start to retreat from a losing battle.

Your ultimate should always be leveled when you can. This skill takes practice to always avoid to cool down with, but does insane damage. Unless the champion your targeting is at deaths door, never initiate with it, as the damage will be minimal compared to a target with stacks of Bleeding.

I choose ignite and ghost for multiple reasons. Let me explain the offensive spell ignite first.

I find Exhaust to be redundant with Darius as you already has a slow attack AND a grab. This is not to say its pointless, but unless every one else of the team grabbed ignite. I wouldn't consider it.

Heal is a viable option if you worry about survival over kill securing and is a good choice when learning Darius.

Ignite helps secure early game kills and synergizes well with his bleed effect allowing to kills when either one or the other alone would fail. It also shuts down Tier champions like Mundo and Warwick.

I chose Ghost over Flash because even if you have a successful flash towards a target, there is still a high chance of them escaping due to your slow run speed of 385. I find that ghost allows me to dive and escape turrets well, as well as offer amazing escape and initiate options. It also works well with Youmuu's, giving me frequent sprints.

Pro's

Insane Damage
Good Crowd Control
Ultimate Deals True Damage

Cons

Slightly Squishy
Mana Hungry (If you land multiple Ultimates, You'll understand)
No Built-in Escape Mechanism