Lion Voltron. If they did the vehicle one I think it would look stupid no matter how fancy the special effects may be. The vehicle Voltron just reminds me of Power rangers. At least the Voltron lions have a better cool factor. Can you imagine CG robotic Voltron lions 40 feet tall ripping up everything like hell? That would look awesome.
As an interesting aside, Peter Cullen, the voice actor behind Optimus Prime also did work in Voltron. He also voiced the Voltron narrator, King Alfor, and Koran. Believe it or not, he also supplies the voice of Eeyore. Who would of thought OP and Eeyore had the same voice actor.