If you use a car cover outside, it will probably do more harm than good. Wind, dirt, and weather will eventually work together to cause the cover to rub the paint. I found that out the hard way a couple years ago when I decided to save 40 bucks a month and I stored the wife's Mustang in the driveway for the winter....I never did get all the scuffs out of the paint by the time we sold the car last year.
If you are covering a car that is stored inside, any cover will be fine. It will just be needed to keep the dust off the paint.
Steve
89