Quartermaster/1.03.24

Empire
One of the most important buildings for the Empire, the Quartermaster offers a lot. Its presence allows for the production of Archers, and through the researching of their three missile upgrades, it makes those Archers actually viable. With Trade, it can allow the Empire to quickly obtain what they want and on demand. And with instant producing Mercenaries, they can "summon" a fast moving, slashing damage dealing unit instantaneously to help counter their enemy's strategies. The Quartermaster can also "summon" some units from other races for additional support and excitement. But one must remember that the choice of unit obtained is random and from a pre-fixed list. (See Empire Researches for the lists of units obtainable).

The building is also small and doesn't require neither gold nor metal to be built, and instead uses the much rarely used crystal as one of its two costs. This makes putting the Quartermaster down in to the Empire's base easy, and considering everything it offers, that's a great asset for it to have. If you plan on using the Foreign Mercenary skills, then you could even build a second or even a third one. But with its main unit instantly produced and researches that'll likely be obtained throughout the course of the game due to their cost, one Quartermaster is usually all you need.

Of course, there are a few issues that come with the Quartermaster, although they're actually more to do with what it holds inside, than the building itself. Firstly, the Mercenaries it can instantly produce are very expensive early game where the Fame skills have yet to be researched. This usually causes the Empire to forego Mercenaries until tier three, or even four. But when against some races (such as Undead), the Empire are pretty much forced to get them early on, which largely hampers their economy. The Foreign Mercenaries aren't much better, it's random what unit you get and the cost doesn't always justify that unit. For example, for 200 gold you MAY get a Leprechaun, but you could very well get a Forestguard instead, still for the same price. Then there's the missile upgrades, while themselves are great, they are mandatory to make Archers useful. Without them, the Empire's archers are only suited to sit in a tower. And finally, the Trade skill is, again, more expensive for the Empire than for the other races, excluding Dark Dwarves, forcing the Empire to fork out a little more for something that some of the other races get for less.