Skyhook is an armored transportation aircraft. It can take on board even the heavier T2 units and easily withstand light anti-air defenses.
Use it to deploy your forces right on the front, especially slower units like Sumos.
It can load 4 small units (footprint 2x2) or a single big one. It's slower, but way more armored than its Armada counterpart.
Skyhooks can survive missile turrets and some mobile AA fire, but fighters, flak heavier SAMs still kill them. Never overestimate their HP.