War machines in Heroes V.

In my opinion, all these machines (except for the catapult and wagon) are only useful in the mid-game—or on small maps—but they are incredibly effective in those cases! The ballista, especially when upgraded, particularly with Delab :D, tears through everyone like a hot knife through butter, and the tent with its resurrection is also very cool. The plague tent is great too, especially with that... Casper, maybe? As for the wagon that boosts shooters' attack and the catapult—those are always great.
Although generally, I don't really like developing machines. They require a ton of money, and in the beginning, every gold coin counts, not to mention there are many other equally useful skills. But the elven ballista is rulez, and Delab, I repeat, totally rocks :D
Another good hero regarding machines is that mage who starts with gremlins. He has all three machines from the start