Over the years, it's been my experience in Mexico that I could hire a car w/driver to be on call during my stay, ready to pick me and mine up and haul us about smartly if not in luxury during my stays. If you're not going to be in the car every day, a little planning can get the price well below what a rental car (with an over-priced insurance/ripoff policy) gathering dust and dents in the parking lot most of the time will run you. Besides, you can learn Spanish, absorb directions and locations, bone up on local folklore, find shopping easier (although often patronizing near and distant relatives of your driver). The downside comes if your driver is disliked by one or more members of the local policia, rurales, federales, parquedores, or the guardia de la noche.

Besides, do you really want to drive with all those crazy, often borracho turistas at the wheel of other vehicles?