[charlesu]

I have had both (actually I used to keep my car covered inside my carport).

Car cover:
Get one made for your vehicle, generic ones tend to blow off because of loose fit (dust can blow under it as well).
Takes some getting used to the hassle of putting it on and off.
Keeps prying eyes from looking inside for stuff to seal.

Car port:
Alows you to work on the car in the sun.
Will not protect your car from morning and afternoon sun.
Wind driven rain still gets in.
Dust and soot will still accumulate on the car.

good luck....