JPMorgan Chase and BlackRock disagree about China's stock bubble. The former says the recent 13 percent share plunge is a reason to buy; the latter sees things "deflating quite rapidly."

So who's right? JPMorgan is correct in the very short run. President Xi Jinping's government has fueled China's bull market and it will do all in its power to sustain it. But in the months ahead, the odds favor BlackRock's take, which is based on the Warren Buffett school of financial analysis.

"The tide is going to go out, and there's going to be a lot of people without their swimming trunks on," strategist Ewen Cameron Watt of BlackRock told Bloomberg Television, borrowing from Buffett's observation about investors caught swimming naked when markets get shaky.