Always under the sun. My cars are always properly protected, with wax and/or sealant on the paint and trim, and rubber conditioner on the rubber parts, so I'm not worried about the effects of the sun; but trees have sap and shelter birds which poop - if you're unlucky, these can eat through any wax or sealant in a matter of minutes, causing etching that might not be completely removable without compromising the paint. This is without even mentioning the possibility of branches or fruit dropping, causing scratches and dents.