A while ago I bought an issue of all the major ones (here), Motor Trend, Car & Driver, Road & Track. They were all pretty boring with only one or two interesting articles each. I found some of the general news interesting, but all the full length car reviews were quite dull.
I skim the car section of the local paper every week, it's always awfull.
Around the same time I was trying out all the major names, I got an issue of Sport Compact Car as well ('cause it had a list of the best 200 sports compacts and my car was number 30 or something). It has a reputation as something ricers read, but I found it was much more focused on real performance, not just looking fast. It was also quite funny in many places and overall a good read. If I subscribed to a car magazine, it would be SCC.
For news and reviews of new cars I read
AutoZine, I haven't seen anything else that compares. I even read reviews of cars I don't care about, just because it's so well written. I know Mark is biased, but I know his biases and I can form my own opinion accordingly. With major publications, I'm always wondering what's actually good about the car and what they've hyped up to please the sponsors (or what's really bad and what they've downplayed).
If I want to hear about how much NASCAR sucks and how everyone running the industry is an idiot, I head over to
AutoExtremist.com. I think they're pretty full of themselves, and they never really have anything new to say, but I still check back every week to see if they've put up something worth my time.