Ford is an internationally renowned car manufacturer. Chevy changes from continent to continent, and in most of Europe is a south Korean car manufacturer called Daewoo, with a Chevorlet badge on it.
Ford have so many credits to their name, as do Chevy. Going back to the the Corvette sting ray, the Ford GT40. The quality of Ford vehicles, in todays market, for me, is better and last longer.
The mustang as Steinmetz stated, is also, in my opinion, a bad example of the abilities of ford. Instead, look to nascar, rally car and formula one, and one would automatically notice that Ford have a broader spectrum and greater reputation, internationally.
Looking forward, Ford have just created a 1 litre engine that can manage 94 mpg, while smashing the time of most super cars on a lap of the Nuremburg ring. That is the future. Meanwhile, chevy had the volt, which has received mixed reviews.
I would have to say, Ford are possibly the best US car manufacturer and will pull further ahead of the pack in times to come.