Here in Phoenix, our public transit really takes the low points, and our taxi service will cost you an arm and a leg just to go a few miles. If I was only spending a day or two, or was in a city like New York where transit is abound, I wouldn't bother with a rental, but for most the the cities I've been to (Seattle, San Francisco, LA, Phoenix), to do much out away from your hotel without having to dole out the dinero or be inconvenienced by late bus service/no taxis, a rental car seems best. Yet, I'm too young to rent one... so I'm stuck with transit, taxies, and super-shuttle to get around if I go off without my own wheels.