Octane. No question. Expensive, but worth it. Great columns by Jay Leno, Sir Stirling Moss, and Nick Mason. Even though UK based, they do from time to time feature American iron.
http://www.octane-magazine.com/
Recently, Motor Trend has launched Motor Trend Classic that is almost a direct copy asthetically of Octane, but the content is not as good. A beef I have with them is that they use photos previousely used in other magazines. Nevertheless, a cheap alternative to Octane.