I've used car covers for years and the ones with the EVO fabric are the best for keeping the crap off the car and provide protection for Hail.
The cotton covers are the easiest to use, but offer only sun protection and a little dust.
The car really needs to be kept clean so you don't scratch it with the cover. I use a wax covered mop for that..
Make sure you place some ID on it as I've had 2 covers without any marking ripped off. (I just put the last 3 letters of my plate or something on it)
Take care, Bill