The life of a gold or porcelain dental crown is very much dependent on personal hygiene. 

Typically, a gold crown will outlast a porcelain crown however this can be trumped by poor hygiene.  The average life span of a crown is 8-50 yrs.  Specifically, a porcelain crown averages 5-8 years while a gold crown can last from 15-50 years.
Gold crowns typically last longer than porcelain as the gold expands and contracts at the same rate as a natural tooth.  This match offers less chance for bacteria to reach the natural tooth.   Gold does not fracture like porcelain and offers a better fit, again reducing chances for bacteria to reach the natural tooth.  Gold is not porous, like porcelain and bacteria tends to adhere to a porous surface.  Porcelain crowns are more esthetically pleasing and are most often placed on the teeth that show in a smile. Most dental insurances cover a crown every 5 yrs.