None of them. Well… all of them. Actually, it’s the wrong question to start with. Digital signage, iPads, smartphones and social media are not the answer to workplace communications. They are just tools and processes that can help you.
There are dozens of products popping up based on one or more of these new products, all claiming to be the answer to your communications problems. For a while they may be popular since they can be very cool and fun. But do they move the needle? Not really.
You can build a house with a hammer, screwdriver and handsaw. You can also go to the hardware store and buy the latest multi-tool band saw /circular saw/drill press. But if you don’t have the right plans in the first place, you’ll end up with a mess either way. New tools can help you do it faster, but not necessarily better.
Workplace communication is like that. Managers who need to communicate do so to build consensus and accomplish objectives. Having the latest app or some new gadget or web service doesn’t matter. Using them to address your particular problems does.
A strong, well thought-out communications strategy is way more important than the latest new thing. Remember, the gadget is just a tool; it’s your master plan that really matters.