Not sure... I've bought less and less as the years have rolled on. I never found the info in them overly helpful, it was mostly just nice to have some light reading around while I waited 10 minutes till a ballgame came on or something. Still, fwiw, here are my impressions of the non-Robert-Kennedy mags...
Iron Man - I've only ever bought maybe 5-6 of these, and didn't really think much of them, but don't really remember enough to give a fair assessment.
Natural Bodybuilding and Fitness - Again, I've only bought these maybe 5-6 times over the years. This may only come out quarterly, because I don't see it that often, I'm not sure. Either way, I never really saw a reason to keep my eye out, and usually bought it on a whim. Two main things going against it, for me anyway, from what little I remember: it is tied to one of the countless natural bbing organizations, so it's that one organization that gets the focus; and two, frankly, I don't much like the way the guys looked. I love that Frank Zane look, but the guys in this mag just looked scrawny. Maybe that's because I've seen too many of the mass monsters and am now conditioned to expect a certain look from modern bodybuilders, I dunno.
Flex - They have Heath under contract, among others. Though it seems like both Flex and MD run articles with pics from the various big stars, regardless of who they're signed with, so there isn't as much exclusivity as perhaps there once was. They seem more mainstream, more commercialized. I think Arnold did return as "executive editor" or some such title like that. I don't think he ever went totally away, it's just that instead of being a "consultant" or whatever he's now going to be more visibly active.
Muscular Development - They have a lot of guys, including Yates, Coleman, Haney, Cutler, etc. They tend to be less mainstream, going into history a bit more for example. The main reason I like MD is that they seem more honest about the industry, even having articles in every issue about steroids and the like. On the one hand, since I don't use that kinda stuff, it sort of does me no good and just takes up space. On the other hand, I like that approach more than some of the other mags, who act like PEDs aren't part of the sport at the pro level, and probably even in many "natural" shows.
I think all the magazines are self-serving or self-promoting to a large degree (they're a business, after all), but I'll say that I've also seen articles in some of the mags, particularly MD, that are honest about the potential dangers of bodybuilding/lifting, even when publicizing it could hurt their bottom line. For example, in the May 2013 issue of MD they have an article titled "What's good for bodybuilding may be bad for your health," in which they discuss what you'd expect from a title like that. Not exactly an article they wanted to advertise on the cover--but it at least shows that they have some sliver of honesty. Sometimes.
Anyway, that's my 2 cents. I've found that going to bodybuilding.com every once in a while and listening to the Pro Bodybuilding Worldwide show once a week (in addition to watching the Arnold and Olympia net-casts) is enough to keep me happy. I still pick up a magazine every once in a while though.