After that video, yeah, I think Garnet would be the best driver.

The Safest Driver: Edward (FFIV) or Safer Sephiroth (FFVII)

The Worst Driver: Oglop Cid (FFIX)

The Most Suicidal Driver: Cid (FFIV) or Zell (FFVIII)

The Driver that wouldn't even know how to accelerate their vehicle: Cyan (FFVI). He had major problems with machinery.

The Driver that doesn't know how to turn: I'd like to say Belthasar from CT because he didn't build wings to Epoch, but since this is about FFs, I'll say Galuf. Instead of turning the meteor to land on a good position, he crash-landed and lost his memory.

The Driver that would break their steering wheel: Cid from FFVII when he gets a level 4 limit break. Hold onto your drawers and don't piss in 'em!

The Driver that would be drinking their car's gasoline while driving: Yikes. Quina (FFIX), I guess.