Axilus Prime

Banshees are a pain in the rear at times, but they aren't very smart. Get one to start attempting to shoot you, by firing on it while close enough for it to think shooting you is worth it. Then, EMP it with the Plasma Pistol and board it. If you don't want the Banshee, simply use it to kill its pilot, then ditch it...and destroy it so no Elites get any funny ideas.

Ghosts are not much of a problem, but as with any vehicle...stay out of its line of fire. They tend to dodge heavy weapons fire, as Ghost pilots seem to be smarter than the rest of the bunch, but a good EMP will clear the way for boarding, grenades, or explosive weaponry. In addition, a Ghost is easily destroyed in Halo 4 with precision or sniper fire being spammed at it.

By the way, Wraiths when boarded from the back will blow up entirely when melee'd. When boarded from the front, however, if you melee only until the driver dies, you can sometimes claim a damaged Wraith. Now, it will die in one hit from any other Wraith's shots, but on Legendary, this makes no difference. You'll die in one hit from a Wraith's shot even with a full health Scorpion.