This is the Jund (black-red-green) deck, and is my personal favorite of the five. In my opinion, it is the strongest of the decks as is out of the box. It is an attrition-based deck that uses creatures as a resource. The creatures aren't usually as big as the ones in Nature of the Beast, or as flexible as the ones in Evasive Maneuvers, but there are more of them. Lots more. And quantity is a quality all its own.
The deck employs lots of token makers to produce enormous armies, and atypically, the deck doesn't tend to use them in the swarming version of token decks that might play things like Beastmaster Ascension, though by all means you can alter the deck towards this sort of thing if you'd like. Rather, it uses them as a resource by sacrificing them, and there is a lot of different ways to get value out of this.
The deck uses creatures to fuel even-the-odds removal with cards like Shattergang Brothers, Stronghold Assassin, Elvish Skysweeper and Quagmire Druid. The idea being that you're prepared to feed more creatrues to these effects than your opponent has, and you'll be fine doing so since your deck has so many ways of recouping the losses. And you are. Thanks to cards like Prossh, Endrek Sahr, Tempt with Vengeance and Sprouting Thrinax, you will almost always have more creatures than everyone else at the table.
Not only will you have more, but you'll have more things to do with them. You can convert them into kill spells as mentioned above; into damage from Blood Rites, Goblin Bombardment, Goblin Sharpshooter and Stalking Vengeance; into card draw off of Carnage Altar, Jar of Eyeballs, Fecundity and Foster. And even when they're dead they're still useful thanks to things like Hua Tuo, Charnelhoard Wurm and Night Soil.
The deck is resilient. It has the greatest capacity to rebuild after a board wipe thanks to various cards that make multiple creatures, and thanks to the myriad of sacrifice outlets your opponents will have a hard time really gaining value by killing your creatures since its a thing you want to do anyway. Most changes I would make to the deck depend on which direction you want to take it, and that is highly motivated by your choice in commander since Jund has a lot of good choices.
PROSSH, SKYRAIDER OF KHER
Prossh. Let me tell you about Prossh. He's beast mode. He is an incredibly powerful flexible creature and commander that I never felt bad about casting. He provides blockers, fodder for your sac outlets, an army for your anthem effects, and when the opportunity presents itself, can general damage your opponents to death out of nowhere. I really don't have anything bad to say about the guy. At six mana, he's at the top end of what I usually like to pay for in a commander, but in a deck built to maximize his qualities, that's a non issue. Prossh is where it's at.
The most memorable play I saw with him was during a four way game. I had cast a particularly large Earthquake, wiping the board of creatures and bringing everyone's life totals to a tantalizingly low range. The Prossh player, untapped drew his card and cast Endrek Sahr, then Prossh, then fed his now enormous army to the Goblin Bomardment he had played earlier killing me in one hit. I never saw it coming, and neither will your opponents.
The Shattergang Brothers represent an interesting option for Jund players. They're not hard-hitting like Prossh or Karrthus or Kresh, and they're not resilient like Sek'Kuar. They are flexible, allowing you to turn things previously not a resource into a resource. They force your opponents to play fairly by making them manage their resources. They allow you to play with fire by giving you a way out of permanents with dangerous downsides like Baleful Force or Phyrexian Arena.
They incentive you to build a flexible reactive deck that attacks from different angles (by playing enough enchantments and artifacts to enable their abilities) and reward you for doing so by blowing up your opponents scary enchantments and artifacts. Any reasonable board state you have that includes the brothers is one that is more capable of dealing of breaking your opponent's board states into nothing.
They're also goblins if you've always felt like building goblin tribal but felt that current options were too weak or boring for EDH. There's so many ways you could take a deck in that direction. No matter how you take it, I would include cards that are fine in any normal deck but really shine with the Gang. Mycosynth Wellspring and Spine of Ish Sah both appeal to me, and Hammer of Purphoros manages to be the only card in Magic that currently produces Enchantment Artifact Creatures, feeding all three abilities.
There are certain strategies that the Shattergang Brothers do very well against; any Voltron deck is pretty much doomed against your ability to force them to sacrifice their heavy hitter since you'll have more creatures than they can afford to feed to the effect, but there are also strategies that will be difficult for the Brothers. Any deck that specializes primarily in enchantments or artifacts is bound to have more than you, who had to diversify, to sacrifice, and likewise creature swarm strategies. But at the end of the day, you have a deck that can carefully react to most any battlefield-based strategies, and sometimes that in and of itself will be enough.
For you collectors out there, the following cards in Power Hungry have new art: