I use the Yankee Gel air fresheners in my car. I drive all day for a living and I like the car to smell fresh and fragrant. I find them pretty good. Some do tend to last longer than others, but they're the best I've found, as I tend to hate the more conventional car air freshener smells. Got a Coconut Bay one at the moment.
I have tried the cardboard car jars, but found although they are strong at first, they don't last as long as the jars. Plus I found them a bit too big to dangle off the mirror, unlike the gels, which are smaller.