In my opinion, MacFormat is the best of the bunch. Very well written, and lots of good technical content. It is pricey, but IMHO, worth it.
To D3v1L80Y's point, the technical reviews of the Macs themselves are always dated by the time you get the magazine. However, the rest of the information presented per issue is almost always of value. Great reviews of software, widgets, printers, cameras, etc.
I personally have benefited many times from things I found in MacFormat, most recently their review of the Logitech Quickcam Pro for Notebooks. This 2 Mp (a real 2 Mp camera, not a 1.3 with interpolation) webcam does not tout itself as being Mac compatible but it is, and MacFormat reviewed it's use with Skype, which is stellar.
I think MacFormat is an excellent publication, and worth the coin. I have sampled a wide range of Mac magazines when I first switched, and settled on MacFormat as the best of them. Buy a few copies at the newsstand and see if you don't agree.
By the way, for you Linux heads out there, MacFormat's sister publication, LinuxFormat, is also an excellent magazine. The the higher degree of "obscurity" that reigns in the Linux world, I find LinuxFormat to be an even more compelling value than MacFormat. I wouldn't be without either frankly.