I have a couple of battery operated chargers that I use for my computer and for my phone. I like these even more than the car chargers since I can carry them with me anywhere, and I don't have to be near any type of outlet. However, I think a car charger would be good too, if I could get one to fit all my devices. That way I could save the battery charger for when I really needed them.
However, if I had to choose one or the other I would stick with the battery chargers I have because they are more convenient.