The real test of reading magazines on a tablet comes down to the magazines' specific apps, and too many don't work well on a tablet. Most are PDF-like replicas of their print layouts, perhaps with the ability to switch to a text view for easier reading but without the accompanying graphics -- that's standard for the Kindle Fire and optional on other devices. I find most magazines on all the media tablets unsatisfying. One major exception is the Economist, whose iOS and Android apps show how it should be done.
Fortunately, most newspaper apps are designed for tablet reading, such as USA Today, the Washington Post, and the New York Times. Newspaper apps on the iPad Mini tend to be more nicely designed, easier to navigate, and more readable than on the Nexus 7 or Kindle Fire HD.
All in all, the iPad Mini is the best book reader, especially if you use the iBooks and Kindle apps. On the Nexus 7, you'll really want to use the Kindle app rather than the native Google Play Books app, because Play Books is hard to read -- a nonstarter for an e-reader.
The playback winner. When it comes to playback options, the iPad Mini wins, mainly because it has the most flexible playback options -- both in terms of output options and playback apps available. If you're looking for a device you want to listen to without external speakers or headphones, you'll again prefer the iPad Mini, whose video playback quality is also very nice.
Deathmatch: Application supportiOS is known for its app selection, and because the iPad Mini uses the same 1,024-by-768-pixel resolution as an iPad 2, it runs every app any other iPad does. Thus, the entire iOS app library is available to the iPad Mini, from games to news readers to photo editors to productivity apps. Plus, if you enable it, your iTunes purchases are kept synced to all your iOS devices.
As a result, you get the best collection of fun and serious apps available for mobile devices for practically any purpose, and Apple's iTunes U library of free courses, aimed mainly at high school and college students, is an amazing resource. That's probably the iPad Mini's biggest advantage: It's not just a media tablet.
The Apple App Store also has the benefit of being rigorously screened for malware, which is not true for the Google Play Store that powers the Nexus 7 and other Android devices. The app selection in the Play Store does not match what Apple offers, but for the kinds of apps you'll want on an entertainment tablet -- gaming, social networking, and information apps -- the Play Store's options are strong. Over the years, Google has strengthened its backup services so that apps you get in the Play Store are available to your other Android devices. The Nexus 7 can therefore double as a business tablet in a pinch.