Ultralisk or Brood Lords?

So far, Zerg games have been (let's ignore ZvZ for the moment) relatively straight forward.  Defend from any harass the Terran or Protoss might throw at you (Vikings, Phoenix, Reapers,  Immortal pushes), expand and macro up your Hydralisk/Roach army and try to out expand your opponent.  Throw in Infestors and sneaky Nydus Networks+Lings and you've got your opponent throwing all their resources into their ground army, trying to wipe out your main army as well as your expansions.

But so far, that Hydra/Roach combo has been working well for the Zerg.  I'm going to go ahead into the future, a time when SC2 is so evolved that Hydra/Roach won't be sufficient enough to hold out against the Protoss/Terran ground army.  A time when *hold for suspense* Zerg needs to use Tier 3 units!

So which direction should we go?  The greatest meat shields ever, the Ultralisks?  Or the ranged destroyers, the Brood Lords?  Well why don't we look at the math first.

The Most Feared Unit in SC1

Okay, the scenario is: We're in late game. Let's assume you've been keeping up with upgrades.  3/3 for your ranged attack and carapace (Cause 'duh, your late game army is Hydra/Roach).  We have just as many expansions as they do, but we keep trading armies, and we need that extra "umf" to break through. Well if we use Ultralisks, they at least start out with +3 carapace armor.  On top of their natural armor, that gives them 4 armor, with 600 HP. 

It takes an Immortal/Sieged Tank ~10 shots to kill that (approximated, because we are assuming upgrades).  I believe the only ground unit that can kill an Ultralisk faster is a Thor (~ 7 hits).  Looking at an Ultralisk's damage, it does 18, plus a bit of splash, taking out Marines, Marauders, Ghosts and Zealots relatively easy.  Top it off with a 60 damage attack against buildings, and you'll understand why the Ultralisk is the Zerg's "toughest weapon".

But is it worth it though?  The Ultralisk Cavern costs 150/200.  Including Anabolic Synthesis (which you seriously need late game), it'll cost you a total of 300/450 to be able to pump viable Ultralisks.  Let's include Chitinous Plating (pronounced "Kite-in-ous", similar to the taxa Chitons), which means you're spending a total of 450/600 to get your "6 armor Ultralisks" (as I like to call them) out on the battlefield.  Unfortunately, 6 armored Ultralisks still fall to Immortals with full attack upgrade in 10 shots (By late game, the Protoss should definitely have max attack upgrade for his army).  Against un-upgraded Thors, 6 armor Ultralisks will die in 8 shots (6 shots, if they are fully upgraded), and against un-upgraded Sieged Tanks, 6 armor Ultralisks die in 11 shots (9 shots, if they are fully upgraded). 

Sure, your Ultralisks could probably wipe out the Terran Marine/Marauder armies or Protoss Zealot/Stalker/Colossus armies (btw fully upgraded Colossus kill 6 armor Ultralisks in 14 shots), but I'm sure you would've done that already with your Hydra/Roach Army.  The scenario I am envisioning involves a lot of Immortals or Tank/Thors, which in combination to the Zealot/Stalker or Marine/Marauder army, is doing well enough to keep his expansions alive against your Hydra/Roach army.  Ultralisks plus your army, without dark swarm, may be able to take out a lot of stuff, but you will most definitely lose a lot of Ultralisks (and at 300/200 a pop, they aren't cheap).

The King of the Air

What if we used Brood Lords?  300/250 to get your greater spire (cheaper than the 450/600).  Though the Ultralisks get the bonus of the +3 carapace upgrade you got for your ground army, you are still saving 350 gas (which you could use for air upgrades!).  Brood Lords cost 300/250, doing 25 damage with 9 range.  If you control them well enough (supporting them w/ your Hydra/Roach; don't let them die easily), you can easily push back the Protoss/Terran ground army and maybe even take out expansions. 

Most Protoss/Terrans don't commit to an air based late game army (or else they'd get run over by Hydra/Roach), so they definitely wouldn't be as prepared for the Brood Lord transition (and what Terran would waste their Mule energy to sweep often enough to see Brood Lords coming).  However, even when they do start making their Vikings and Phoenix to combat your Brood Lords, don't forget you still have excess Corruptors (that you are about to make into even more Brood Lords) to fight! Corruptors do 12 damage (+10 against massive, but I doubt they'd have the economy to make enough Battlecruisers/Carriers to be worth a damn), and when microed in conjunction with your Hydra/Roach army, can easily protect your Brood Lords.  Don't forget the Corruptor's added bonus, of its Corruption spell, letting it disable cannons and Planetary Fortresses (making expansion killing all the more easy).

If it does come to it, an un-upgraded Viking (cause who can spend money on air upgrades and still be this far into the game against a Zerg) needs to shoot 12 times to kill an un-upgraded Brood Lord (16 if you have full air carapace).  A un-upgraded Battlecruiser (with its puny 6 air damage) needs to shoot a Brood Lord 69 times before it can kill it (I'm serious, the Brood Lord's natural 2 armor is so damn sexy).  Of course, the Battlecruiser's ability to one hit K.O. with a Yamato is a nice balance, but if you let the Terran mass up that many Battlecruisers, and conserve that much energy, and upgrade Yamato, and be able to wipe out all your Brood Lords...well then I don't think you deserve to win!   

A Protoss un-upgraded Phoenix needs to shoot 46 times to kill a Brood Lord!  Correct me if my math is wrong: A carrier does 5 air damage (x2), but the Brood Lord's 2 armor means it will only do 3x2 damage per interceptor.  It would take 46 interceptor attacks (although they are pretty fast) to kill your Brood Lord.  The Mothership is probably the best, able to kill it in 12 shots. 

Now don't forget Marines and Stalkers can probably do a lot of damage to your Brood Lords, but this is SC2: Use your Roaches and Hydralisks to help fight! Roach/Hydra can handle stimmed marines better than lings did in SC1.

Of course, no one says you can't upgrade your Brood Lords before you reveal them.  Even though air attack is quite benficial (+3 with each upgrade, giving you a grand total of 34 damage after all three upgrades), you should have sufficient attack power with your Hydra/Roach Army.  The Brood Lords are really there to give you extra range and the ability to harass from areas of no terrain.  Therefore I am quite sure that Air carapace is more important, to keep your Brood Lords alive.

The added bonus of using Brood Lords, is that if you micro well, your opponent's troops would attack the Broodlings.

Do not make the mistake of falling into the habit of BW's use of Guardians.  Back in BW, you would harass a bit with Mutalisks, and then quick tech Greater Spire and morph Guardians in the air, able to take out natural expansions or other units.  This left the Zerg open to a counter attack, since so much resource went into the Guardians.  Guardians wouldn't usually have a late game presence, simply because much of the gas went into Defilers and Ultralisks, not to mention the overwhelming fear of irradiate and storms (though for SC2, even though storms have been nerfed, do watch out for them).

In SC2, you can get a good economy running before you tech your Brood Lords, and at that point, you can join them up with your army, able to move out with one giant ground/air ball.  The Zerg's strongest ability is being able to smoothly transition multiple tech trees.

For maps that have close by expansions, like Kulas Ravine, LT, or maps with close bases, like Desert Oasis and Scrap Station, Brood Lords work amazingly.  You can pressure an expansion, and then quickly fly back to defend your main, while you expand.  You never have to take an open field direction to harass SCVs.  However when your opponent gets a strong enough anti-air system going, then you will have to start travelling with your main army to pick off expansions. 

So far in all the games I've witnessed with Brood Lords, Protoss seems to be the one most unable to deal with this strategy.  But then again, Zerg don't always seem to need Brood Lords.  But practicing them now gives you an advantage for a time when they do.

Alright, Thanks for taking the time to read my Guide! Comments are very welcome. Hopefully in about 24 hours I get an SC2 Beta key, and can start writing up Guides detailing races that aren't just Zerg.