This one came very close! You begin in a laser testing chamber, and things go horribly wrong (in true Half-Life style!). Rushing out and up into a control tower, you get to see the Osprey swooping in to replenish the supply of grunts. Lay low and wait a short while, and a hanger in the far corner opens and (my favourite bit!) an Apache rises out! Great stuff. Both aircraft have well-tuned paths. The Osprey makes precise banks and there are no collisions.
Be careful what you do with your ammo though... this is one tough map! Apart from its difficulty, there's actually nothing wrong with it. As I said, it was a close call, and Devil Mesa edges into first place thanks mainly to its extras.