I've had subs to Rider, Cycle World, and Motorcyclist longer than some here have been alive (I even used to read Cycle; now get offa my porch!). I've also sub'd to MCN, Backroads and RoadRunner (since 2nd issue) for many years. I began subscribing to the Iron Butt mag as a non-member when the first issue came out a couple of years ago. I get Sport Rider free each year or else I wouldn't have a need for it; I think I've been getting Motorcyclist free the last few years or I likely wouldn't pay for it anymore. I also spend the big $$ to sub to UK's Bike and Ride, but they're worth it -- I wish the American mags would come anywhere close to the content and vibe of Bike and Ride; those guys still seem to have fun riding, kinda like Cycle and CW in the old days.
If forced to narrow it down, I'd want Bike, Ride, Iron Butt (tons of great info that's also applicable to we non-IBAers) and RoadRunner (for touring content only.) MCN would be mandatory but for having Bike and Ride, whose bike tests are far more thorough than MCN and yet still seem very objective considering they're not ad-free, and there are some differences in spec between UK and US bikes to take into account.