"I'm choosing the fastest car in the world."
Translation:Yo elijo el carro más rápido del mundo.
That's only the case with people; it's called the "personal a". And it's not strictly an elegir bound phenomenon. https://www.thoughtco.com/the-personal-a-preposition-3078139
You would translate it that way because you have the apostrophe to use which Spanish doesn't. On the "del mundo" thing. Spanish uses what we see as "of the world" where "in the world" is more common in English. As I have put on many forums the "correct" preposition is not math. What we perceive as THE RIGHT ONE is a matter of common use. The first one to drive me crazy was" Pienso de ti." but there are many "near misses" between languages. "It's just more of the "What is your name?" and "He is six years old" and "I am thirsty" that you just have to learn. (Look 'em up if you don't them yet!) Good luck!
Ken, I've tried to figure that out, too.
First, I don't think you would say "el carro más rápido del mundo* because "the faster car in the world" doesn't really make sense.
Second, I think you would need something to compare the car to, at least implicitly. So, my conclusion is that it would be Elijo el carro que es más rápido que el otro, or at least Eligo el carro más rápido.
Perhaps someone more knowledgeable could help us out?