I wouldn't call this a fad. Things are only going to grow as more users establish themselves, and I could totally see people starting their own live shows. But there’s the question of what happens when people start streaming sex, drugs, or harassment. How will that be handled? Vine allowed x-rated content in its early days, and banned it about a year after it launched. Will things like that attract users, or drive them away? People are already streaming movies like Fast & Furious 7 while they're sitting in the theater, but companies have been surprisingly cool about it so far.
If you're thinking about jumping in to live-streaming, while both apps are solid, I'd have to toss my recommendation to Periscope. It's less cluttered, and, well, I'm already using Twitter—and since Twitter is its parent, it's likely to stay around for awhile. I wouldn't be surprised if Meerkat sells to Facebook or Microsoft sometime in the next year or two. Whatever you choose, watch out for your data plan—this shit will gobble it up in no time—and be on your best behavior, because you'll never know when you'll be on camera, live.