Most Wall Street analysts, eager to sell stocks, pull their punches when faced with questions that might lead to uncomfortable conclusions. But Bernstein Research’s Todd Juenger and MoffettNathanson Research’s Michael Nathanson have proven their fearlessness over the years — which is why I was so pleased to see both out this morning with thoughtful reports that reach different conclusions about a key question: How much longer can the go-go period for media stocks last? Shares have been on a tear for the last three years largely because moguls stopped using cash to build empires choosing instead to slim down (as News Corp/Fox did, and Time Warner is doing, by unloading their publishing units and CBS is doing with its billboard ad business) and returning cash to shareholders. Stock buybacks in particular “have been enormous,” Nathanson says, with Viacom cutting the number of outstanding shares by 21% followed by Time Warner (-17%), Discovery (-16%), Scripps Networks (-12%), News Corp/Fox (-12%), CBS (-11%), and Disney (-6%).

Juenger warns that this strategy is about to run out of gas. Interest rates will rise at some point, making it expensive to borrow for share repurchases, And companies will want to hang on to cash as the number of pay TV subscribers begins to fall, ad growth slows, content costs rise, and revenues from streaming video companies led by Netflix begins to “flatten or decrease.” That leads the analyst to divide the industry into two categories: There are “Organic Growers” such as Discovery, Fox, Disney, and AMC Networks. They’re strong “in the most attractive segments of the Media business, especially international markets.” But he’s concerned about a second category, “Buybackers,” that includes Viacom, CBS, and Time Warner. Their stock prices have grown faster than their earnings alone would justify, he says. As a result, “the time is ripe for a mini-rotation back in favor of the  higher quality media names.”

Nathanson’s more sanguine. Buybacks should “continue for the foreseeable future,” he says in his 149-page report initiating coverage of Big Media. He’s also optimistic that for the next two years or so things will be fine in the industry’s core pay TV business. Networks will be able to squeeze higher payments from cable and satellite companies, with fees expected to grow on average about 10% a year through 2015 vs 2.2% for advertising. He isn’t “envisioning a collapse in this profit rich ecosystem.” As for the movie business, Nathanson doesn’t mind the studios at Disney, Time Warner, Fox, and Viacom: They’ve cut expenses including the number of releases enough to maintain their profit margins even though he projects “flattish domestic box office revenue in 2014 and 2015” due to what he perceives as a “lack of confidence” in upcoming releases.

Broadly speaking, though, Nathanson notes that “we just can’t help being a bit nervous about the level of comfort and certainty that investors now hold for the group.” He has a “buy” recommendation for Disney, Viacom, and AMC Networks but is just “neutral” for CBS, Fox, Time Warner, Discovery, Scripps Networks and Netflix.