No distracting sun spot or reflections. Plus a simpler background (although I would choose something that wasn't a similar shade with the car, but better) with less distractions.
The thing to think about while doing "advertising" is that the car is the star, right? You are trying to "sell the car." So, while backgrounds certainly help to make the shot more interesting, they should not take focus away from the car. Plus, you want the car to look as "clean" as possible, in that you don't want odd relfections, streaks, etc impeding people'* view of the car. That'* why when you see some ads nowadays in magazines etc, the cars look very uniform, almost computer generated. The idea is to allow people to appreciate the car for what it is.
EDIT: and it is a more interesting angle.
1990 Pontiac Sunbird LE 2.0L OHC - 5 spd - 96HP!!!!!!!!!! - 35+ MPG - World'* Ugliest Hubcaps - Sunroof - Alpine deck..........0-60?.......YES!
1994 Pontiac Bonneville SSEi Gone but still in the family...
Pics... Pics...Pics...XM Install...