So, I've just returned from a two week trip of Andalusia (Southern) Spain, and for the first time on a trip like this I rented a car. (Full disclosure: actually I once rented a jeep for a week in Belize, but as there were no buses - nay, barely ROADS - it doesn't count) Usuallly I make use of the excellent public transportation system available, but since I had a lot of ground to cover, I decided to go mobile.
The Verdict? Undecided. It didn't really cost me that much more to rent the car than to take buses/trains wherever I wanted to go, and it WAS quicker, if you didn't factor in the time lost while (frequently) lost. Fortunately there are apparently no traffic police in Spain, so my occasional (constant) flouting of No-U-Turns, red lights, and Pedestrians Only signs went unpunished. (One afternoon I got so frustrated in trying to reach a parking garage thru the maze of donkey-wide, one-way streets that I simply gave up and drove completely across a pedestrian plaza - just cruised right past people at cafe tables, old men on benches, small boys peeing in fountains). And I did like being able to pull right up to my hotel and dump my bag, instead of getting off in some train station halfway across town, then humping my gear uphill (it's alway uphill, isn't it? usually both ways) to the hotel. And I definitely didn't miss dragging my gear to said train/bus/mule station, only to find I'd just missed the last ride out for the night.
On the downside, I got taken to the cleaners by the parking garages - in Madrid it was 20 euros a day to stash my car - and I spent a lot of time worrying that something would happen to the car itself that I would have to pay for. I made some unwise driving decisions - at one point thinking I could drive from Seville to Tarifa at night, realizing after an hour that the directions were too confusing to deal with in the dark, and having to go back to Seville. I used taxis just as much in the actual towns as I would have had I not had the car, since the streets were so narrow and difficult to navigate. And the car gods wreaked their revenge on my liberal interpretation of the law by guiding me to the one illegal parking space on a square in Ronda, resulting in a trip to the impound yard and a 60-euro fine. Those whom the gods will destroy, they first make park in a tow-away zone.
So all in all a mixed experiment. My next trip may give me the opportunity to test it again... we'll have to see.